I’ve just watch IGN’s video review on ME2, it’s noted that the story in ME2 has heavy reference from the 1st game. So for those that have not played the 1st. I suggest you play through atleast the main quest only. Though some side quest has connections to the main story it’s not entirely necessary.
Improvements in ME2:
1. Class has been revamped for better replayability
2. Better exploration – notably space exploration
3. Each side quest now have their own environment to explore in; unlike the 1st where 90% of all side quest environment are the same.
4. Better menu & inventory layout
5. Elevator rides removed
6. Slow loading texture in ME are not presence in ME2
7. Customizable armor/gear
Con:
1. Rare crashes, Glitches



