Sonic Adventure one and two are some of my personal favs of Sonic. I liked the gameplay and it wasn't that frustrating once you got use to it. I use to despise Eggman/Tails levels, but they are quite fun when you get the curve down.
Cajole didn't the "adventure fields" in Sonic Adventure one take like 5 minutes between boards tops?
I agree with Himuro that Shadow sucked ass hard, however the Wii game looks like shit, pure shit.