Have you ever gone off and played all of the games in a series or franchise in a row?

I honestly think it's really fun. I went on a Metal Gear spree a while ago and played them all in
chronological order. (And I mean ALL of them. Starting with 3, then on to Portable Ops,
Peace Walker, Metal Gear 1, MG2, MGS 1, 2, 4, and ending on MGRR.)

Right now I'm going on a Metroid spree. I just beat Zero Mission 100% in under 2 hours and I'm working on 100% scans and pickups in Metroid Prime right now.

Why don't you guys tell me about your sprees/marathons?

Oh yes!  I love doing just this!  I've done this with so many series I doubt I could remember them all if I tried, so I'll just mention a few of the more memorable ones.  I've done it with the Final Fantasy series around the time the Gameboy Advance versions of the games came out (Ran through 1-7 over about a two month period of time).  I played through the first four Dragon Warriors back on the NES back in the day.  I finished up a playthrough of all the Fallout games a few months ago (Wasteland, Fallout, Fallout 2, Fallout: Tactics, Fallout: Brotherhood of Steel, Fallout 3, and Fallout: New Vegas.), and most recently I've been carving my way through the Elder Scrolls series from the beginning, I just started Skyrim a few days ago.

I think the most impressive speed run I've ever made is when I beat Fallout: New Vegas in under six hours (Primarily done with skill checks, zero combat except for what I ran away from, and with more than a little time mapping out my path before hand) that I mentioned in a different thread a few days ago.

I tried this with Pokemon when Diamond came out. I bought the game and told myself that I was going to beat one game from each gen before I play this one. The game was very tempting and I really wanted to play it, so I did... After beating the other games. It took me about 3  months, but it was so worth it, though I am never going to do that again. The next time a game I want comes out, I am playing it right away.

Not exactly. Once I played Sonic 1, 2, 3 and Knuckles but I never played beyond that because I don't have all the Sonic games.

I've done this with the Assassins Creed games. I own all of them and a digital copy of the first one. I'm a huge fan of the Assassins Creed franchise so the games are fun every time I play them. I still need to play Assassins Creed Black Flag. I've heard a lot of good things about it from close friends. I might have gone on a Tomb Raider and Resident Evil spree when I was younger but I don't really remember.

Yeah, I usually do a Paper Mario one every once in a while (other than Sticker Star, since I lack the 3DS).
Partly because I love the Paper Mario games, and partly because it's the only series marathon I can properly complete.

Yeah I do that a bit. I will get in the mood to play nothing but (lets say) Sonic. I will hook up my Genesis/CD/32x and play Sonic for weeks and nothing else. The last time I did this it was with Namco games.  If I enjoy a company or game I will try to play all they have.

I've only ever done this twice. The first time was with the Pokemon series once Platinum came out. Well, it might not count since I started from the Ruby, Sapphire, and Emerald days up to Pokemon Platinum. It took a good long time to complete the games though, and I'll have to say that it was pretty fun to replay all the games again. I was actually able to sit through the games because it was a fresh experience again, especially have a sort of "refresh" with each successive game. The other series would be Bioshock. When Bioshock Infinite came out I played the first game on my copy, then Bioshock 2, and then Bioshock Infinite. I can probably say that it wasn't worth it though, as I'm not a great fan of Bioshock. Still, it wasn't a bad experience overall, and I had fun playing a majority of the games in each series. 

I love doing this all the time. I recently did it with the Devil May Cry series playing it in chronological order. I also love doing this with The Legend of Zelda and Sonic. It is always so much fun when you play through the entire series in a short amount of time.