Even if you have played Gears 2 without playing this one, you'll still get some fun out of it.
Bad: slow loading times, a couple glitches where your character can become stuck (only happened once in this game, but has also happened to me in Gears of War 2), blood/gore looks relatively fake compared to everything else.
Online: I have never been a big fan of Gears online.
Overall: I had originally just watched the cut scenes from Gears 1, so I could play Gears 2 (on Xbox360) a while back. Just recently I thought I'd play the original Gears. If you haven't played either Gears games yet, definitely play this one. Even if you have played Gears 2 without playing this one, you'll still get some fun out of it.