if you've not played it before, which sounds like you haven't, buy it. Possibly/probably the game of last year. Almost certainly the strongest game in terms of story, infact, it just was, strong graphically, gameplay is nice though I played witha 360 pad I can imagine a mouse is way better for it. I hate almost everything of late, and there are downsides, most of the driving is awful in the game, almost everyone agree's on that, i did all the sidemissions pretty much when I played but really theres little reason to do so, if you skipped all the sidemissions it would be a brilliant game and plenty long enough.
One of the best value games of the last 2-3 years based on price vs hours to complete the main story let alone the side stuff.
Just buy it, being that its one of if not THE best game of recent years its a brilliantly writen story from Bioware who have a huge pedigree in these games(kotor games before this) and this is the first of a trilogy of games on the story. Its not a sucky trilogy where you get one story, split up and stretched out, its a story heavy game with a great finish, as in it feels like a great ending, not just a cliffhanger that makes you want to smash your face in because the next game is over a year away(hl2 series like). Will most likely turn into the best trilogy ever made on the PC which means you really don't want to miss the first one