Pretty much the best burger I've had in about 8 years... been there a few times now, and they are consistently good. As others have mentioned, cash only... Also not cheap.. but simple and really good for what it is. I suggest going later in the afternoon, or get there around 11 or slightly earlier, they are packed during lunch/dinner, but 3:30 if you do a late lunch or early dinner is pretty mellow.
Onion rings are great, as is the fried zucchini and the fries are decent too.