I am big on the bistro circuit. When Avenue B first opened, I had an incredible meal here. I've been back a few times now and definitely enjoy it. Most recently I had dinner here during Restaurant Week.
The food is great and it comes with a refreshing amount of creativity each time you visit. They use a giant chalkboard to let diners know about the daily menu that goes above their more consistently available items. I'd recommend heading for the chalkboard unless you're really pulled toward something on the main menu.
The service here is generally great although our server last week was a bit pushy. I felt rushed and definitely felt pressed to buy above and beyond the set restaurant week menu. She could have been a bit more friendly for sure but our food courses were spaced well, which is a big service pet peeve for me if it gets botched up.
Bottom line: if you want some upscale dining without busting open your wallet too much, Avenue B is an excellent choice. BYOB makes it an easy place to spend under $100 and still splurge for dessert!