I've played a lot of mainstream pokemon games. I love them, but I'd like to try something different for a change. Could you give me some examples of Spinoff Pokemon games I should try and why you think they're so good?

NintendoTails : There are some really interesting ones I can think of just the top of my head.

Firstly if you want to try something in the RGR a few examples are

Pokemon Pinball: Well this one's pretty self explanatory it's pinball but with Pokemon, it's simple but very entertaining if you like pinball and Pokemon, there are various games.

Pokemon Trading Card Game: There's a game for the GBC based on the trading card game that follows a somewhat similar style of the original Pokemon games but uses a map to instead directly go to different gyms, it's fun if you like the TCG and is also a good way to learn about it, though it of course is a bit old so it only includes the older Pokemon card expansions.

If you're willing to actually spend money on games there some other I can talk about:

MY FAVORITE SPINOFF SERIES:

Pokemon Mystery Dungeon series: There are several but if just starting I'd recommend one of the older installments actually specifically Explorers of Sky or alternatively if you can't find it, Explorers of Darkness or Explorers of Time.

They're basically a dungeon crawling game with a Pokemon spin on it as instead of being a trainer you lead a party of Pokemon through dungeons and learn Pokemon moves as you would in a regular Pokemon game. They offer a lot more challenge than regular Pokemon games IMO and at times I even enjoyed them more than I do the main series games. Even if you haven't played a dungeon crawler they're a great way to start.

The games I recommended in particular also have great but still family friendly storylines, a lot better than those in the main series games and even genuinly sad at points. There's a lot of content too the only gripe is the gameplay can get a bit repetetive especially after one playthrough but I still HIGHLY recommend it.

Pokemon Conquest: This is a spinoff I haven't personally played mostly because I haven't been able to get a hold of it as I skipped on it because of the price tag when it came out. But I've hearly only good things about it. It's basically fire emblem tactical RPG on a grid based gameplay but with Pokemon instead. Probably a good choice if you're looking for something strategical (though Pokemon Mystery Dungeon can be as well). I can't say too much though since I haven't played it but check it out if it sounds interesting.

Pokemon Snap: It's an n64 game and should be in the RGR but isn't for some reason. Basically though it's a game about taking pictures of Pokemon and you get higher scores based on how good the pictures you take are. Sounds boring I know but it's suprisingly complex and fun when you try it, so if you can find a copy I encourage giving it a chance.

Pokemon Ranger series: Well I figured I'd mention it since I've played one of the games. I personally didn't like this game that much though, the story is decent, but the actual gameplay bored me. Basically you play as a Pokemon Ranger helping people in need by temporarily getting the help of wild Pokemon draw rings with the stylus around Pokemon on the DS so most of the time it isn't that complex but you may still like it if just looking for a decent story involving Pokemon, I'm actually planning on reviewing it some time in the future. Really though I'd recommend one of the other options before it.

I really recommend to play one of the Mystery Dungeon games. Most of the games include many of the Pokémon available and the stories are amazing. One of these Mystery Dungeons is playable on Vizzed, Pokémon Mystery Dungeon Red Rescue Team. You can play as one of your favorite Pokémon and you can explore various dungeons. The best Mystery Dungeon game is Explores of Sky. So if you have the money, I really recommend it to buy the game.

I don't get it why it is so underrated though...

Other great series are the Ranger games and Pokémon Conquest is really fun as well.

As the users above me have said I would recommend Pokémon Mystery Dungeon: Explorers of Sky. It is really a great game where you get to pick any of the starters from generation 1 to generation 4. You can also choose Riolu, Shinx, and a couple of other non-starters. Then you get to pick your partner. Overall, I think the plot of this game is better than any mainstream Pokémon game. It is very sad towards the end with Primal Dialga and all that, but the overall ending is happy. This was my first Pokémon game and it brought me to close to Pokémon. (I heard that they are in the process of making a new Mystery Dungeon game.)

I would also like to recommend Pokémon Ranger: Guardian Signs. This is because I loved this game's plot as well. On top of that, it is extremely challenging (at least for me, it was) and takes some time to complete. However, when you beat the game you get great satisfaction. 

That being said, I haven't played those kind of Pokémon games in a long time as I have grown addicted to mainstream trainer battling elite four games.

The pokemon series has loads of great spinoff games to choose from, with a great variation of genres as well. I'll list you some spinoff series I think you should try out.

Every Mystery Dungeon game EXCEPT for Gates to Infinity. The other users who've posted here have already mentioned this series, but I'm going to go a little further with it. The Mystery Dungeon series usually starts with you answering a quiz. The answers you give will determine your nature, thus determining which Pokemon you'll become. Every mystery dungeon game has this except for Gates to Infinity, which lets you choose your starter. Afterwards, you get to choose a partner pokemon to join you and together you create a rescue team. (or in Time Darkness and Sky, an Exploration team.) There's loads of pokemon to choose from, including all the starters up to the generation the games came out in, as well as a few other pokemon. The only exception to this is Gates to Infinity, where you only get 5 pokemon to choose from: The Unova starters, Pikachu and Axew, while in red, blue, time, and darkness you get 16 to choose from, and in Sky, you get 21 pokemon to choose from, though 2 of them can only be your partner. You'll explore many dungeons that change every time you visit them. These dungeons can require lots of strategy to get through. Making sure you have a good variety of items is essential. Having apples can help you keep you from getting too hungry. If your hunger meter drops to 0, you'll start losing health with each step you take. That's why having apples is so important and can add to the challenge of dungeon exploration. Unfortunately, this feature was taken out of Gates to Infinity (except for a few dungeons), which is one reason why Gates to Infinity is so bad. It's way too easy. There's plenty of other interesting items in this series, including orbs, which can have interesting effects on the map, yourself, or enemies, also seeds are another essential type of item, especially the reviver seed. Without reviver seeds, it'll be nearly impossible to navigate through the toughest of dungeons. All Mystery Dungeon games have excellent storylines, something that other pokemon games usually lack.. Laly the entire series has fantastic soundtracks, including Gates to Infinity. Like I said earlier, I'd stay away from Gates to Infinity and play the other games instead. One of which can be played on vizzed, Which is Red Rescue Team for the GBA. There's a new game coming out soon called Pokemon Super Mystery Dungeon, and from the trailer, it seems that the apples are back, and there are once again many pokemon starters and partners to choose from. All the starters, as well as Pikachu and my personal favorite Riolu.

If you're into tactical RPG's, then you'll love Pokemon Conquest. It's the best tactical RPG I've played besides Fire Emblem Awakening. I normally don't like tactical RPGs, but Pokemon Conqust is an exception. The one issue I have with that game is the fact that your pokemon only get to use 2 moves. There should've been more moves to choose from. Other than that, Pokemon Conquest is an awesome game that all tactical RPG fans should try out.

Pokemon Colisseum and Pokemon XD: Gale of Darkness: This spinoff series is definitely the closest resemblance to the mainstream Pokemon games. The main difference here is that the games only have double battles, and wild pokemon aren't common at all. Instead, you steal shadow pokemon from various trainers by throwing poke balls at them. If you're looking for somehting similar to mainstream games, then these 2 games are for you. They're both for the Gamecube FYI.

Pokemon Trozei: A puzzle series where you put for pokemon together to make them disappear. This game is pretty fun, and it's cheap, though it's only available on the Nintendo Eshop. It's a pretty good spinoff game if you like puzzle games.

Pokemon Ranger: This DS series revolves around you circling your stylus around pokemon to capture them to help you perform certain tasks, such as removing barriers or putting out a fire. The gameplay can kinda get repetitive after awhile, but it has a pretty good story, so that's a plus.

Pokemon Snap is an interesting photo snapping game. I didn't play this one very much, so I really can't say much more than that. If you're into snapping photos, then you should check this out.

As Zlinqx already said, Pokemon Pinball is pretty much what you'd expect: pinball with pokemon. If you're like me and you love pinball, then you'll love these games a lot. They can each be played right here on vizzed.

Last but not least we have the Pokemon Trading Card Game, which Zlinqx mentioned This one doesn't have multiplayer, but it's still an extremely fun game. It has one really awesome song in it, it's the club master theme, which can be found here: https://www.youtube.com/watch?v=uOmHl6lmi5U

That's pretty much a rap on awesome spinoff games. I hope you found this helpful. Good luck with deciding how many of these you want to try out. I'd personally say you should at leas try out the Mystery Dungeon games

I saw some videos on pokemon conquest and I would definitely recommend that.

You're basically a warlord who has to take over enemy castles and fight against Nobunaga.
The gameplay is really interesting so you should definitely check it out!

I think most of them have been said that I could recommend but the second Pokepark game is good. The first one not so much. But the second is actually really good. I agree with the prior responses though the Ranger games are great. I have two reviews for them one on the first one and the third one Guardian Signs. Also Sky is great too. I currently have a team of Phanphy and Meowth as my main and partner. We are Team Gem!
Coliseum and Gale of Darkness are great but not made by GameFreak but are really amazing. Darker plot then the main games. Conquest is great too.

The Mystery Dungeon series. Really haven't played the later installments tho. Only thing that sucks is based on random questions about yourself, you get a random Pokémon to start with as you, but you get to choose your partner. Other cons about the game, in order to get new Pokémon are by random asking to join your team, having the right habitat by buying the location and money is a little scarce in the game unless you sell something you don't really need in your bag, plus speaking of bags, you only have room for about 20 items, and not like 20 different items, I mean 20 items. Like 10 rocks and 10 apples. Tho it's a good storyline about you turning into a Pokémon and the Pokémon can talk. It's a fun Dungeon RPG, but unlike the tradition Pokémon games where u have a good amount of PP, Mystery Dungeon has half the PP of each move. Still a good game.

I would recommend Pokemon mystery dungeon. I find it more convenient than trying to catch all known wild pokemon.

I recommend Pokemon Mystery Dungeon.... Generally. It's one of the few Pokemon games I've seen with a deep plot. (The others being Pokemon B/W and X/Y.) To me, every PMD game is very good, the crown jewel being the Explorers trilogy. Red Rescue Team and Blue Rescue Team are both very good, but are outmatched by Explorers. Even though many people might think Gates to Infinity was a huge dissappointment, but it's still decently fun, it still has a heavy plot, and has a lot more features than the first 5 games. Take the series for a spin, because it's really the most popular Pokemon Spinoff that you'll find out there, PokePark being the second most popular.

It's a close one for me between Pokemon Mystery dungeon and Pokemon Trading Card Gaming.

Pokemon TCG is pretty old now, and it's way out dated in comparison to newer games - but it's still brilliantly fun. If you like the idea of collecting cards and what not, I'd go all in on that.

The mystery dungeon is a very fun spin off. If you like Digimon World (I think it was a Playstation One game), you'll love this game. Plus, it's pretty cute in all honesty - and you get to be a Pokemon. What's not to love about that?