they used an interesting technology for their graphics (voxels basically), so even then it looked a bit rough compared to full-3D shooters. but it return it allowed for huge environments. if you can look past the graphics and can find a good community to play with, I'd say do give it a try, its co-op holds great moments.
but frankly, even ArmA 2 Free provides more content and features today, so if you're looking for a good game to pass the time ArmA 2 has everything you need (but I'm sure you know that already)