For a small airport, CMI is a 4-star airport. It can be described in one word: breeze. Everything is easy here - checking in, the friendliness of the people who work here, getting through the smallish concourse, boarding, deplaning, taking off, and landing. As for public transportation, I can't vouch that there is a public bus from Champaign-Urbana to the airport, having either parked there, or having been dropped off or picked up.
The one thing you might notice is as you pull up to the terminal is that the facade looks like the cross section of a plane's fuselage and its wings, yet done in a manner that doesn't look in the least bit corny.
This airport exists largely for one purpose: to serve the University of Illinois flagship campus and the towns that sprung up around it. It does not have a Champaign address, but Savoy is almost immediately south of Champaign and the campus area. The contrast between CMI and Chicago O'Hare is startling - going on a puddle jumper from a small airport, flying over sparsely populated agricultural land and, in about 30 to 40 minutes, looking at the Chicago skyline from high above and landing at O'Hare, where the hustle and bustle of the world's busiest airport and your connecting flight await you.