That does not give you a lot of time. IAH is in the middle of a vast wasteland, so unless you decide to cab/rent/public transport it, your choices are limeted.

There is the express bus to downtown, but there is a premium for that. IIRC there's a mall not too far away that you can get to by public transportation.

I'd stay at the hotel and get some rest - watch a movie, surt the internet.

EmailKid