I have ventured off of campus to Farren's 3 or 4 times and each one has been a great experience. As many have said, the burgers are all very good though a little expensive for a student's budget. For the student crowd, I would definitely stay away from the Kobe Burger as the extra cost isn't justified by any increase in flavor. The Buffalo Burger is one of the best burgers you can find in C-U and is definitely worth a try.
Outside of the Burgers, Farren's has many unexpected dishes which are all delicious. I have tasted both the scallops and toasted ravioli, both of which I was leery of at first, but each of the dishes proved to be delicious. Don't be misled by the word "pub" in the name of the restaurant, everything on the menu is a specialty.
The place is small so the service is always quick and the atmosphere is always very casual and friendly. All considered, a burger (or scallops) with a bottle of your favorite at Farren's is one of the best lunch picks in downtown Champaign.