Sonic Adventure 2 is a so-so Sonic title, and even hardcore fans of the Blue Blur such as I may not even enjoy it.
Sonic Adventure 2 is, obviously, the sequel to Sonic Adventure, and it improves and un-improves on its predecessor. Gone are the pesky adventure worlds that were confusing and annoying. However, an even peskier thing takes their place - you are forced to play as multiple characters.
Now, the first Adventure game had multiple characters as well, but you weren't forced to play them - you can beat the game as only Sonic. However, this time around Sega decided to force players to grind through terrible mech and treasure hunting stages. These stages are longer and more annoying than the Sonic and Shadow stages, and they really slow down the game. I'm not sure why people complain about Sonic Unleashed's Werehog stages and then love this game.
Thankfully, though, the Sonic and Shadow stages are pretty good, and while they're not the best 3D Sonic gameplay, they still hit the spot for good ol' platforming action. The story of this game is also a plus, and while the voice-overs are absolutely horrible and the animations are very clunky (even for the time this game came out), the final story moments are really well-done and memorable. The game is also quite challenging at times, and the final levels can be a real pain (or a joy, depending whether you like challenges where you have to die and restart the whole level all the time). I will say that some deaths I had felt like more of the developer's fault than mine, but maybe that's just me.
Since I'm reviewing the Battle version of this game, I'd better cover those features as well. SA2 Battle comes with a great multiplayer "battle" mode, and while I was expecting some kind of arena thing, the Sonic stages are actually multiplayer races, which are a blast to do. The mech stages are just arenas where you shoot against each other, and the treasure hunting stages are a race to see who collects the most Chaos Emeralds first. The Sonic stages are by far the most fun, and it makes getting the Battle version worth it. However, there is not a multiplayer version of the 1-player campaign.
While Sonic Adventure 2 has not aged nearly as well as other games of this era, it still is worth playing to this day. The forced stages are very pesky, though. And worst of all - you can't play as Big the Cat! No fair!
...I'm just kidding.