When we think about Sonic Adventure, or really any old game/ system, we tend to block out the negative and focus on the positive. That's nostalgia for you. It may have been a great game for its time, but the recent XBLA port shows we should have taken it for what it really was, a big "Trouble Ahead" sign indicating what was on the horizon for the blue speedster. Oh, and the port doesn't help much either.
Sonic Adventure is a slightly tweaked version of the GameCube version. The visuals hold up as well as late 90's 3D can, even at HD. Unfortunately, there's no widescreen support, forcing you to view everything through a blue-bordered window. As with other games, Sonic Adventure runs blazingly fast, so its not like you'll really have the opportunity to see anything without a healthy dose of blur, but the option would have been nice.
One of the few "Thank the Maker Nothing's Changed" moments is the soundtrack. The one great constant in all Sonic games is the music, and Sonic Adventure delivers on every front. Of course, the voicework is still the same - but you can skip through it.