We've gone to Big Al's a few times and each time has been great. I've only tried the 60/40 burger (60% beef, 40% bacon), which is excellent, as well as a few bits of the guacamole burger, which was also very good. The fries are tasty, and possibly worth splurging and getting the fancy ones with truffle oil, parsley, and parmesan cheese. The first time I had a milkshake that was on special, and it was excellent--something with a lavender flavor. Hopefully they make that a regular one.
If you're in Old Town and need a quick bite, this is a good place for you.