This game has beaten the Neverwinter Nights series and is now the greatest game I have played.
The story is amazing. Maybe not as epic in scale as the original Mass Effect, but it plays out in such an amazing way its hard to describe. Best part, each time you play through you can really alter the story, even to the point that your actions in the course of the game will affect which one of your team mates will live or die at the end. Even the main character may perish. Due to this, the game has tremendous replay value.
The best part in my opinion, are the characters. I LOVE the characters in this game. Rarely you feel so attached to fictional characters. It actually hurts when one of your team mates dies. As with everything in this game, the characters behaviour and opinion of you changes as you make different choices, so some may be loyal, others disloyal etc.
The game-play and graphics are great. Maybe not revolutionary, but you can't complain. There have been several improvements since Mass Effect 1 making the gameplay more enjoyable and not as repetitive. The characters are more alive now, the environment seems more real.
So yeah, this is my number one game of all time. For now at least.