Played Mass Effect through on the xbox, loved it.
Now own one and two one Steam, and am in the process of playing them in preperation for three.
While I haven't played two yet, my biggest reservation comes from the ammo clips (from what I have heard they are scarce and irritating), and also just lack of micro managing (again, from what I have heard).
I think for the gun system, maybe have ammo clips to take heat, fine. But then if you run out, you can fire like in ME1, with overheat and such. Sounds like a good compromise to me. Or toggle between the two modes, control is always nice.
But I had a blast with ME1, the sheer depth of the universe just sucked me in. So many interesting races with cool backstories. That is what really brought me in.