^I seriously advise you to go on a media blackout until you've finished the game. A lot of people will try to spoil the ending for you and it's something you really ought to experience it for yourself.
Actually, what I'd really advise is to go get ME1 & 2 and play through them first so you can import you saves. Starting an new game on ME 2 or 3 from scratch is a shadow of the experience you get from developing your Shepard across all 3 games. I'm pretty sure they're both on sale on Steam right now, so there'll never be a better time.