Very good

They really, really need to fix their video vsync code. It's horrible.

The New Version, 2.1.2 is terrific. FCEUX developers respond to the majority of bug reports. This is the best NES emulator out there. Thanks to Adelikat for addressing the savestate request :)

When I was playing Megaman 3, the ROM suddenly crashed (black screened) while I was in the Snake Man stage. I checked the ROM addresses using the Debugger tool and I found it to be stuck in a forever loop. This is most likely caused by the video desyncing or something else happening. This problem needs to be fixed.

FCEUX emulates NES games no problem. It's got lot's of features and I recommend it.