Mass Effect is an all around good game with only a few minor problems in frame rate and game length.
The universe is not actually as big as you might think, you can't land on every single planet you see. Which was a bit of a dissapointment on my part but did not get in the way of enjoying the rest of the game. Another small complaint is the lack of different enviroments, if you've landed on one ice planet you have landed on all of them.
The combat is a complete innovation for rpg's, it has a cover system which works rather well and the guns have an awesome amount of power behind them which makes mowing down your enemies pretty satisfying. There are powers your character has called biotic powers, kinda like force powers in star wars, that are hard to use in the begginning of the game but they grow on you and eventually become another enjoyable part of Mass Effect.
The graphics are amazing in Mass Effect, characters and enviroments are highly detailed. The only drawback to this graphical awesomeness is the framerate which occasionally slows down during intense firefights and other moments that call for extreme rendering.
The game is actually pretty short, my first playthrough was at almost exactly 30 hours, but i can guaruntee that you will not see everything the first time around which calls for multiple completions and makes the game fun every single time you play it.
Overall Mass Effect is an amazing game that is definately worth buying if you love a game with a good story. If you have ever played another Bioware game you are in for a treat with Mass Effect.