There are very very few Sonic games I haven't played and don't own. In fact, other than Knuckles Chaotix and the Pico games, I can't think of any.

As for Generations... it'll be a day one purchase for me for certain. I kinda liked the demo, as stated earlier the jumping felt a little sluggish but I'm sure it can be worked out in time for launch. It actually feels like the kind of game Sonic Team would've made in 1991 if they'd been able to, which is a good thing. And it bears more than a few similarities to that Sonic Fan Remix that got everyone nerdgasming a few months back.