I agree with ielah, I'm finishing up my undergrad and 5th(!) year here and the difference between the cultures in grad students and undergrads is very different. I would say its not as bad as hornedfrogmeg (from TCU I assume) makes it sound. The student body is also large enough (almost 50,000) that you will find all types if you look hard enough, even if the overall stereotype is very conservative. I've also noticed every year seeming a little more diverse than the last, and I think each incoming class is more liberal than the last (maybe not by much, but I believe it is true).
I've noticed that you are doing political science and would probably be applying to the Bush School of Government, that department is housed in a building far from the main part of campus (right next to the Bush Presidential Library), which means while you're on campus, you'd only be dealing with people in the polisci and econ departments. The little area by the library is actually very pretty, much nicer than the rest of campus.
There isn't much to do here except drink and the music scene is mostly Texas country and local student rock bands. Northgate is not a bad little area of bars and restaurants, but not your typical "downtown." You might also want to check out some places in downtown Bryan (The bar Revolutions comes to mind) as it tends to be a little more older and some places more "liberal" crowd. Like ielah, I've enjoyed my time here but I'm ready to leave, just look at the schools I'm applying too...most are more liberal cities than college station! Downtown Austin and Houston are a 90 minute drive away (the outskirts even less) if you need a city and both have good cultural stuff (Austin is the "live music capital" of the world, Houston has great theaters and museums) so its really not that bad. Also, google MSC OPAS, we do get a few broadway type plays every year coming through.
Anyways, if you really like the program I'm sure you would be fine. I would just imagine it would be bit different than what you are used to.