I've been playing Mass Effect 2 for about a month now. Unfortunately I'm a PS3 owner so yes, I've never played ME1, and I really wish I had. I've been able to piece together most of the backstory from reading on the internet but I know that a lot of the dramatic effect of some scenes is lost to me.
Aside from that it's a great game. I'm enjoying it more than the other game Bioware put out last year (Dragon Age: Origins) because the interface and menus are a lot easier to navigate, and combat is better. The maps and areas are thankfully small but plentiful. Too many games put way too much space into areas that you'll never need to visit.
But I can't help but compare it to every other sci-fi game/TV series I've ever seen, especially Star Wars. From the whole extra-galactical race threatening to wipe out everything, to most of the alien races and even the whole BIOTIC thing (reminds me of the Force a lot of the time).
Even though it is a better game on most fronts I still like Knights of the Old Republic better on the sole reason that it's Star Wars. If Bioware ever makes a Star Wars game this calibur then it'll probably be my favorite game of all time.
06/20 -- Bolt Thrower
07/06 -- U2
07/10 -- Incantation
08/07 -- Faith No More
08/22 -- Motley Crue
10/03 -- Origin