Ignore the haters.
I loved this school from the minute I stepped onto the campus for my college visit. It was the only college I applied to, and I miss my undergrad years there immensely. It was a time of great growth and experience, and it really is what you make of it. If you apply yourself and make an effort to reach out, have new experiences, and make new friends, you're going to have a great time.
Join a student organization, or better yet, start one. Find some ethnic cuisine you've never tried before. Skip the campus bars every now and then and try out downtown Champaign. Pull an all-nighter in the UGL. Go to your professor's office hours for a change. Pick up some B movies at That's Rentertainment. Play intramural sports. Get a job at a dorm dining hall and make lifelong friends. Watch some kids play Dance Dance Revolution extremely well in the Illini Union. Read a book of poems on the Quad.
I'm not a frat bro. Nothing like one. And, though Illinois has more than its fair share of them, you definitely don't have to go Greek to love UIUC.