Sonic mauls down soldiers aboard a helicopter, bursts out, grabs a piece of metal, then pretends he is leaping onto a mountain to snowboard. He ends up boarding down a hilly street, ploughing through many cars along the way; wreaking absolute havoc. Not exactly the friendly Sonic we all know. Sonic runs into Shadow the hedgehog, and realises Sonic's capture was a case of mistaken identity. A few levels later, Tails flees from the cops, destroying many cars in process. Later on, Sonic and Tails hijack the President's limo. I'm sure they'd end up with the death penalty with this kind of behaviour.
There are two options in the menu; Hero or Dark. In the Hero story, you play as Sonic, Knuckles and Tails. In the Dark, you play as Shadow, Rouge and Robotnik. In each story, you alternate between the characters and they each have a different play-style.
Sonic/Shadow's levels are based on speed, with a bit of platforming. Sometimes the level's are designed for a visual spectacle so sometimes all you are doing is holding forward and letting Sonic run though the loops or bounce around on the bumpers. This may look good, but is very boring.
Knuckles/Rouge's stages are hide and seek. You have to find 3 emerald pieces and you are given clues where they are. A radar shows you where one of them is at any time using a “hot and cold” style feedback. So you can be stood next and emerald but the radar suggest you are no where near. So if you want to take advantage of the radar, you have to do them in the order the radar wants you to find them. Knuckles can run really fast which isn't a helpful trait since you need to slowly travel the stages and keep looking out for emeralds. If you die, then the emerald moves position which can be a good thing or a bad thing; some locations are easier to find than others. The emeralds aren't usually in plain sight, so sometimes you have to destroy objects to find them. These levels last way too long are often infuriating.
Tails/Robotnik is in a mech and can shoot bullets and homing missiles. The combat in these stages are a bit mindless. Rings restore your health bar. The attack makes an awful high pitched ringing sound, and you will be using this attack constantly. It's best to mute these stages.
Boss fights are either too easy, or quite clunky. Some fights seemed inconsistent whether the boss would take damage, or I would.
The camera is still very poor. It tries to guide you through the levels but is designed to always push you forward. There's occasions where you need to backtrack slightly, but the camera doesn't really adapt. You can manually steer the camera, but then it will just reset. You can only move it left and right, but with Knuckles/Rouge, you often want to look up and down.
Finding the Chao key in the levels gives you access to the Chao garden when you have finished the current level. You are supposed to raise some creatures called Chao. I say “supposed” because I had no idea how it worked. Every time I visited the garden, all the animals and items that I placed in the garden had gone. Many people seem to love this feature, but it's a bonus rather than the main content of the game.
One massive improvement over the first game is that the Hub world has been removed. This was an incredibly awkward of moving to the next level.
The voice acting seems better than the first game from what I remember, but it is still poor. The characters often talk over each other or is very mistimed. The music is also set too loud which drowns out some of the dialogue. The music is bizarre as always, often with Hip-Hop style tracks.
Sonic Adventure 2 is marginally better than the first game. It still features poor level design, poor camera, poor sound. There's not much fun to be had here.