For a kids movie, I liked the first one a lot. I sooo dreaded going to see it and was very pleasantly surprised.
2nd one didn't do much for me. Maybe because I don't know the VGs all that well so didn't appreciate Knuckles and Tails. Seemed like a lot more CG chars and less real people compared to the first. Did James Marsden even have 10 min of screen time? Not that I am some huge fan of his, but his interactions with Sonic in the first movie is what made it work.
Kids absolutely loved it though, which I guess is all that matters.