Super Street Fighter II Micro Player Pro

The built-in screen is tiny but sharp enough that I can actually see what's happening during fights, which surprised me. I've been playing it on my lunch break and the four new stages look great for a handheld this size.

The four new characters and stages add real variety to the classic fights, and the screen is sharp enough for quick matches on the bus. My only quibble is the shoulder buttons feel a bit cramped after an hour, but that's a small price for portability.