Originally Posted by Iron Ape
It's a pretty lengthy game, and to get the most out of it, you need to play through a few times to engage in all the different possibilities that are available, plus there's a male and female path to take which adds even more paths to take.
If you play for 3 days solid, you might get through it once. I started playing ME2 (also on the PS3) back in January and I've managed to play through twice with a male character, and I'm about 75% through my first female character. I'm planning to do one more female and another male hopefully before getting 3 (which is out at the end of the week here in the UK).
If I were you, I'd get to stepping, since 3 comes out in just over 5 and a half hours in the states!