the sennheisers are by far the better headset. the game one are open design which will have a wider soundstage while the game zeros are closed which will isolate you a bit from the outside world.
if you want a cheap game one.. you could use a hd518 headphone, xonar dg soundcard and the modmic. that would total $154 and give you a similar sound profile, virtual surround and good mic.
how does the hd518 compare to the hd598 that the game one is based on? slightly bassier, slightly less soundstage, same exact drivers used, somewhat worse build quality and not as nice pads. its a cheap mans hd598.