This is a good game and i think that the next game that is made by the developers could be one of the finest that i will play, unfortunately this game really has no lastability and so will be completed in hours rather than days and will be sitting on your shelf soon after.
Renting this title would be my advice cause it certainly is worth playing as the weapon mods are very nice and fun to try out on your unsuspecting enemy. Play this game alone also and maybe switch between cut scenes rather than playing co-op. The lagging graphics are not the only niggle as the AI seems unaware there are two of you and so player two can often just walk up to enemies and blow them to pieces in comical fashion!!
Thats where the fun ends however. Im not sure about P.C users but on the xbox myself and my friends who play xbox live found this game an utter disapointment.
Over all the single player game feels ok, a little rushed in places, most enememies react the same all the way through the games various (samey) environments.
Weapons feel highly underwhelming and although the ability to upgrade each weapon seems like a good idea, it only really makes the somewhat weak rocket launcher feel better.
Vehicles handle the same, whether they hover, have 3 or 4 wheels, or way 10 tonnes.
Map maker has limited options which is shame as this seemed like a great idea.
online play is fun for an hour with some friends, but gets boring very quick with the very limited match options.
Final verdict, steer very clear of this one, stick with Halo 2 and Unreal championship 2!