"What can I expect" is a pretty broad question.
If you're talking about college life in general, well, college is what you make of it. I made my college experience lots of football, plenty of running and working out, and enjoying myself with a couple of really good friends.
If you're talking about PT, field training, and the like, that will vary from school to school. It's best to talk to a Marine option student or the AMOI where you plan on going to school and finding out from them.
If you're talking about summer training, your first summer is done at CORTRAMID. I don't know what it stands for but if you poke around the site some you'll find plenty of discussion on it. It's basically an intro to different areas of the Navy, and a week with Marines. Training during your second summer varies. Several different things you can do. The summer between your junior/senior years (your last summer before you graduate) you'll do OCS. Yes, it's as hard as people say it is.
Having seen several classes of new Marine options come and go, I will offer this advice. When the NROTC staff (and student staff) tells you they expect something of you, don't screw it up. Be on time. Don't look like a fart sack full of doorknobs. If you have trouble with something, let somebody know and get help. Most of all, learn something and have fun. Yes, it is possible, regardless of what some students might say. Good luck!