First and foremost...if you are an engineer this is an excellent school to go to. The whole school revolves around that. Same for business. If you are a science major than the course load is no joke and if you feel like you can be happy here than its not a bad choice. If you are anything else MAKE SURE you ABSOLUTELY want to go here because the school really does not care about other majors.
So now for the types of students. Most people are in state. The school is very diverse. There are also a lot of internationals, asians in particular and they tend to stick together. Most come to study in our renowned engineering school. I'd say greek life is HUGE here and its how most people make friends if they are into partying and stuff. If you aren't super outgoing or planning on going greek, making friends might be tough at first (unless you luckily get a good floor). I lived in ISR which is more of an antisocial dorm and I had a terrible freshman year experience because of that, but even then I still ended up finding my niche in that dorm and made a tight group of friends. I love it here now, although because i'm not outgoing I still find it difficult to find research/club opportunities. If you dont want to go greek I HIGHLY recommend any living learning community because people tend to bond with their floors. If you are hipster/intellectual/liberal/artistic/musical/theater type I HIGHLY recommend living in Allen. With making friend here in general just put yourself out there and eventually you will find something that works. There are a lot of them there but you have to be a go getter.
The thing about clubs is that there are literally thousands, but not many are run well. You really have to search to find a well run club, and eventually through classes you will hear of stuff. Personally for me, it was hard to jump in like I wanted to, which goes back to the making friends thing too since being in clubs is how you make friends.
The administration is terrible. Lack of communication, organization, accommodations. No way to appeal professors, financial aid, grades. its a bureaucracy, essentially. If you want to turn a form in you have to go to 20 different offices, people, etc its horrible:/ You have to learn to not trust the administration with anything.
I've had good and bad experiences with professors. My MCB professors and TAs were all amazing and understanding. They were all TOUGH though. My classes are big but I'm still an underclassman so maybe it will get smaller. Some classes though, especially in chem for non majors, i've had terrible professors. Chem has been a constant nightmare for me having to teach difficult material to myself...i've only had one good chem teacher so try and go by rate my professors, although sometimes for that you have no choice. Gen eds and stuff..I went by rate my professors and some were good some were bad. In general they are strict though so pay attention to the course policy.
Counselors and deans depends on the college, but my experience with them has been that if you reach out to them, you will find one good one you connect with. In my college I met with several terrible counselors before found an amazing one that has inspired me so much.I know it sounds like i'm bashing U of I but I love it here despite having a terrible freshman year. I think what makes it so rough is you get thrown right into things and no one really explains how things work. I highly recommend this school for certain majors, but only if you do your research first. Figure out what you want out of college and BEFORE going there make sure to plan ahead and you should avoid some of the pitfalls I fell into and love it there from the get go.