Sadly, the story has very little to do with its exceptional prequel, but its plot does still stand on its own merits. Eggman has broken into a military base in order to obtain information about the abandoned space colony ARK which his grandfather was involved with because he hopes that he'll be able to use it on his way to achieving his goal of world domination and building Eggman Land. While there, he runs into Shadow. Sonic, meanwhile, has been mistaken for Shadow and arrested (despite being a world-renowned hero), so he escapes his captors but then has to avoid the military.
Like last time there are six playable characters, but sadly only three different play styles. There are two stories, the 'Hero' story and the 'Dark' story which, as you may be able to guess, tell the story from either the point of view of the heroes or the point of view of the villains. The 'Hero' story has you play as Sonic, Tails and Knuckles; Sonic has regular, speed-based levels, Tails (in his transformed aeroplane) has third person shooter type levels and Knuckles explores giant levels looking for shards of the broken Master Emerald. The 'Dark' story has you play as Shadow, Eggman and Rogue the Bat (I find Rogue rather annoying). Shadow plays pretty much the same as Sonic, Eggman the same as Tails and Rogue the same as Knuckles.
I think it's quite a shame that they made all of the characters match up like that, as it spoils the diversity that the first game had. Notably, the speed levels with Sonic and Shadow run a lot more smoothly than the ones in the last level (barely any glitches) but while this is an improvement, Tails and Eggman feel like worse versions of Gamma (from the last game) and the levels that Knuckles and Rogue have to explore are far too big, they're huge and mostly without interesting features, making their levels quite boring. Sonic Adventure 2 also lacks any kind of hub world, which I think is a shame; the levels simply play one after another with cutscenes in the middle. The upside of this is that it allows for a different kind of storytelling and a narrative with a greater sense of tension. On the subject of tension, things get a lot darker this time; for once I actually fond Eggman threatening (I normally just love him as a comical, ridiculous villain).
A Chao Garden is featured again and I believe that it has been improved. A Chao will now change physically depending on who raises it; a Hero character will make Chao look white and angelic, whereas a Dark character will make a Chao look black and demonic. There are more mini-games for the Chao to play and it just feels generally expanded. This time, in order to access it, you just have to collect a Chao Key in the middle of a level, which means you are taken their automatically and so will probably go there more often (prompting you to use this feature more). As always, the Chao are extremely cute.
Like the first game, Sonic Adventure 2 also features an enhanced Gamecube version entitled Sonic Adventure 2 Battle. I have to admit that I've actually only played the Gamecube version, but they're not too different from each other so you shouldn't worry about which version you get. The game has a small multiplayer mode (where you can race or battle another player) but it's nothing special and this was expanded slightly for the Gamecube. The Chao Garden can also be linked to the Gameboy Advance Sonic games with this version. The only real downsides of buying that version is that the Dreamcast one had several hidden cameos from Big the Cat, and these were removed (for some reason) from the Gamecube one.
The game may not be quite as good as the first one, but, I still like it very much. Rating: 8.7/10