Went to a large public school with 28,000+ undergrads. Loved it.
Pros:
very wide variety and quantity of available classes
wide variety of majors and fields of study
many different research labs and options (I spent a while in a neuroscience lab and also in a microbiology lab)
hundreds of student organizations
good pre-med adviser
Division I athletics
gigantic library with tons of places to study, huge student union with lots of places to get food, study late into the night, bowling alley in the basement, theater on the 2nd floor, art gallery on the 1st floor
pretty diverse student body, find whatever clique or group of people you want
Honors college with good scholarships, small classes (12-15) with full-tenure professors in topics of their specialty
+/- factor
Large classes - I liked them, honestly. I never had a lecture class that I thought had too many people (biggest was 300)
Cons:
classes taught by TAs
you can walk across campus and not see anyone you know
not as much scholarship money (but tuition wasn't that high anyways)
non-honors students might have trouble getting into a specific course if it fills up