My opinion on Sonic Adventure 2:
It's a pretty good game. Far from the best Sonic game in the series (imo that honor goes to Mania Plus) but Adventure 2 still has its perks. Sonic and Shadow's levels are all fun to me, the mech stages are tragically underrated (blowing things up gives me a good sense of euphoria), and the extra modes are all fun to me and give the game good replayability. I also must say that I love the controls. They feel as smooth as butter to me.
However, half the treasure hunting stages are far too long, but that's not the worst part of the game. The worst part of the game is the crappy camera. The treasure hunting stages are at least fun to a certain extent. But the camera, on the other hand, infects every single level of the game. It makes levels a little harder, it makes bosses a little harder, and it can even make the extra modes a little harder and frustrating, and it's all for the wrong reasons.
OVERALL SCORE: 7.5/10. Definitely not perfect but has a lot of charm to it, and to be honest people have screamed "OVERRATED" and hated on it to the point where to be honest, I think it is overhated and underrated. But, other 3d Sonic games have definitely improved on SA2's flaws by a good margin. Colors comes to mind as an amazing 3d Sonic game.