Graphics
The graphics of Sonic Adventure are absolutely stunnning. 
Because of the power of the Dreamcast, the level of detail
is much higher than that of Zelda 64. Levels are crystal
clear, and aren't blurry in the slightest. However, there is
one important problem that is worth mentioning. The camera
does act kind of odd at times. In some levels, it's 
perfectly fine, and won't cause any trouble for you at all. 
But in a certain few levels, it can seriously affect your
enjoyment of the game. Basically, you might not be able to
see what's happening around you, causing you to lose for no
good reason. 

Game Mechanics
In the game, there are several playable characters,
including Sonic, Tails, and Knuckles. The story for each
character is different. Only by beating the game with every
single character, will the story make complete sense. 

Each one of these characters has different abilities that
are unique to them. For example, Tails can fly for short
periods of time, while Amy can attack enemies with a giant
hammer. Sonic can move at incredible speeds. While the
different characters play the same levels for the most part,
they do have different objectives. Tails' objective in most
levels is to beat a  Controlled Character (Usually
Sonic) to the end of the level. This makes each character's 
quest unique, and more fun to play. 

The best way to explain the level system, is by saying that
each character's game takes place in a different part of the
same 10 or so levels. In the Casino level for example, Sonic
must go to the different games to get rings, in order to
proceed to the next level. Knuckles, however, must fly
around at the top of the level, in an area not accesable to
Sonic, to find three hidden Emeralds. 

Sonic's quest is about twice as long as any of the others,
and is the most fun to play, overall. Even so, most of them
are pretty enjoyable, with the exception of one or two. 

Game Play
Game Play in Sonic is very different from, for example,
Mario 64. There are a few similarities, however. The levels
are linked by things called 'Adventure Fields'. Those are
different areas in the game, in which you can talk to
people, and do simplistic puzzles. By talking to people, you
find out what you need to do to get to the next level. The
problem is that clues are very abstract, and it can be
annoying to figure out where to go next. 
 
Levels in Sonic go by at an extremely fast speed. In fact,
at some points, you feel as if you have no control over
what's happening. Levels are VERY straight forward, with few
places to explore. Because of that, the game isn't as
challenging as some. In fact, most of the time, it isn't
challengine at all. For most of the game, you have a set
destination (The End Of The Level) and must get there as
fast as you can. 

Music
For the most part, the music isn't impressive at all. In
fact, it can get very annoying at times. Most of the voice
acting is simply terrible. I hate listening to it after a
while. I really feel that the developers should have spend
more time in this area. 

Overall
Sonic is not a bad game. It's about average. It's fun to
play for a while, but then you will probably lose interest,
and move on. It's not the kind of game that will keep you
glued to your seat, but it has it's moments.