Wow. Where to start? This game has a rich storey line, memorable characters and great game play.
You customise the main characters appearance (even down to the gender) which is a feature more games should have as it helps make them more immersive.
All of your decisions and your actual character carry through to Mass a Effect 2 and 3 which is a great game mechanic and means that everybody has a slightly different experience.
Although the graphics are starting to show their age I highly recommend buying this game as it will ensure you get the most out of the Mass Effect trilogy.
Bad points - graphics are starting to show their age. Controls aren't as intuitive as on later games. Unable to romance Tali (you can in the sequels though so it's not a complete loss).
Good points - everything. Rich storey lines, fantastic characters, free choice, huge environment to explore, the ability to carry your character over to the sequels (which are as good as this game but with better graphics and controls). Just wow. Very immersion. Many addictive. Such awesome. wow.