I actually completely forgot about Dark Brotherhood which is a shame because I did like it. I love turned based RPGs and multiple choice responses, so while it was not nearly as in-depth as I would have wanted (and I hate combat that requires my input for moves to work) I had fun with it even when I had to replay a large section. Only actual bad points I have is needing to do those stylus tricks sometimes perfectly or fail the move (ugh Cream), the soundtrack is dull and some of Sonic's responses were pretty wildly out of character, though that's the nature of multiple choice dialogue.
Sonic Battle for the Gameboy Advance was another one I forget about but really liked. I freely admit its repetitive and some of the challenges in story mode are just ridiculous with a weak Emerl, but I just love the story!
Since nobody mentioned Advance 3 yet, I'm going to let out my opinion.
Of course, it has a lot of stuff that can crush you, there are bottomless pits abound, and the chao are hard to find, but I still kinda liked it. I liked the partner system and I think it has the best soundtrack of the Advance series. In short, there's a charm to it that makes me come back to it.
The only Sonic game I played was Adventure & Adventure 2. I LOVE that game. Unfortunately I didn't like other Sonic games I've tried, I don't really like platformer in the first place.
Ugh, now I really want the game on Steam but not sure if I can have as much fun playing it on PC without a controller...
Man SEGA is in a really, really big slum. I read they're mainly focusing on PC/Mobile games now, barely making a profit, and had to hand out a ton of job layoffs. I don't expect to see a new Sonic game after Boom unless something changes. I agree with this one guy though. It would be cool if Nintendo bought out SEGA and just turned the whole franchise around.
I really liked Sonic Heroes, but nothing beats the Original 4 games for genesis... I never played any of the bad ones, because I heard they were terrible ahead of time lol