Sonic Generations was pretty good, and Sonic Colors wasn't that bad either.
Day levels in Sonic Unleashed and 2D levels in Sonic 2K6 were okay.
I haven't played the really really really bad ones (sonic vs the black knight, etc), but I don't think the franchise has really fallen as far as everyone jokes about. Among my friends, Sonic is still very much cool, but I suppose most people don't blast hydrocity zone music in their car like us.
I would like to live through it just so I can see things like Sonic Underground on the air again, and I do miss it, but not enough to really be longing for it.
While I miss Sonic being cool, I think I miss other things being cool more, like the days of Mechwarrior/Earthsiege/G-Nome/Shattered Steel giant fighting robot games being "The thing" and also Wing Commander/Xwing vs. Tie Fighter/Tachyon the Fringe sort of "Space Combat Simulator" games being mainstream. I also miss turn-based combat things like Jagged Alliance, X-Com and Fallout Tactics...
That said, if I could get one thing back, it would be FPS games that are outside, fast-paced, great level design, etc...I guess Tribes:Ascend will hold that for me, but I would like a REAL duke 3D sequel (Not Gears of Duke).
But Sonic....Yes, I would love to be the cool underground "Sonic" lover who got all the girls because the kids talking about Mario were losers...