I have found myself to replay Sonic Adventure once every two or so years. I enjoy it greatly. The story mode feels limited at first, but after a while things start to play out.
Amy, Knuckles, Gamma, and Big's storylines are fascinating and one of the most in depth the series has given them.
Big's gameplay is similar to Sega Bass Fishing, however I had found myself needing to reset the game once or twice due to some model clipping of the lure and getting stuck behind the wall or floor.
The music may not be many people's favorite of the series, my spouse had complained the theme to Windy Valley was too bright and busy for him to enjoy. I'm thinking the music mixed in with the sound effects of the stage environment was more bothersome. A few songs I do love is the Chao Race Entrance music, Mystic Ruin theme, and Gamma's theme, all composed by Fumie Kumatani.
Also, comparing to the Director's Cut release of Sonic Adventure, the models in the original version are much more pleasing. I like the matte texture of the characters, along with the fact a lot of graphics with transparencies were buggy in DX.
Anyone who hasn't touched Sonic Adventure, I highly recommend the original Dreamcast release.