I'm happy to report that I used fceux a couple of days ago to play some NES games, and whereas previously it had a couple of odd rough edges, this time it worked perfectly and smoothly, including fullscreen and saving/restoring states.
And the most important thing of it all, it allowed me to configure the cross-shaped joypad in my controller as the directional input. Previously it only detected the analog joysticks, and it is really hard to play platform games with analog joysticks!
In theory it also supports entering Game Genie codes for those of us who cheat a bit (sometimes), but I haven't tested it myself (YET!).
fceux is packaged in the community repository so you are just a
pacman -S fceux
away from playing with your favourite games! Go go go go!