Sonic Unleashed was the most tolerable for me.

I liked Sonic Unleashed the Day stages were phenomenal and the night stages while not as good as the day stages wasn't as bad as people made them out to be according to me and I did have fun at times (but the battle music got REALLY repetitive real fast). I did dislike the final boss battle though.

There was a "dark age" in the 2000s? I thought the "dark age" was the sub par GameGear games, like Sonic Blast and Sonic Labyrinth, as well as that Game.Com swill. 

I honesty enjoyed all the ones I played, and I'm sure if I had a Wii or a DS, I would have liked the others too.

I honestly don't see why a lot of people don't like Shadow the Hedgehog. Besides the plot and minor things, I actually really like it.

I really hate this 'multi-voting disabled' because I found more than one of these games tolerable.
Lemme see,
-Shadow the Hedgehog was tolerable because the gameplay actually didn't glitch out too bad on me, and it had a great soundtrack. Most of the other things in that game left something to be desired, though :/
-Sonic Riders was actually a lot of fun, and so was the sequel. One of my favourite racing games, actually. I'ms urprised they even tried with a story for a racing game, to be honest. I'm pretty sure Transformed doesn't have one.
- Sonic and the Black Knight wasn't the greatest, but I enjoyed it a lot. I only rage quit for a bit when I couldn't beat King Arthur that one final time. It was other wise just fine, as long as you aren't as close minded to change as some fans tend to be.
As for the other three, I either didn't play them (Unleashed and 06) or I just flat out hated them (Secret Rings).

Sonic Heroes was tolerable to me. I think it is good in my opinion.

Where is sonic heroes in the poll? Believe it or not that's my favorite sonic game in the sonic franchise! (I know, I've read the topic and it says 2005-2009)

Since shadow the hedgehog is on the list, might as well pick him up. I mean, 6 years ago (or more) me and my cousins used to play it a lot and we had fun owning the enemies with guns we get at the end games, we also liked the mission system and because of it we actually finished 5 different endings in ONE day....yep, that's how fun it was to us (and know when I look at it, I wonder how we liked it in the first place).
We even used to challenge one another to beat a certain stage/boss with a better rank than their (and in case rank A, we compare scores for stages, times for boss fights).

Sonic and he secret rings is actually a very good game that I enjoyed. Also sonic and the black night was also great.

Along so my favorite game of all time,shadow the hedgehog.

Sonic and the Secret Rings. Yeah, it wasn't "good", but it was way better than the abominations of '06 and unleashed. I actually had FUN at some segments.

The only dark age for sonic was the classic fan boys whining and moaning because it's not black eyes, personally sonic was fine, his handheld releases were the "dark ages" seriously only advanced 3 is worth a damn, the rest of the library is trash.

A lot of you might not agree, but I thought Sonic Riders was the best! I loved the whole idea of the air board racing thing. I could really really see Sonic enjoying this, and I really got into it. I liked the story, the new characters, and I liked the levels and music. The only thing that bugged me was how difficult it could be, but then again I like challenges. When I beat this game for the first time I was so thrilled!! Because it was so damn hard!!! I beat it on both sides, though playing as Jet and his team was considerably more difficult. I also really like Jet. He was a cool character. I hope he'll appear in some new Sonic game sometime. I don't like Zero Gravity though. The concept was really dumb and I couldn't get a hang of all the controls.