Bionic Commando - Elite Forces
(also there's an older mono game, which is close to the NES version)
the mega man games are like remixes of the NES originals as well, if I remember correctly.
Dragon's Lair - based on the arcade (really!) - look at this one!
Donkey Kong GB - after you pass the 3 or 4 levels based on the original arcade, the "real" game begins.. another nice one.
Perfect Dark - similar to Metal Gear - can't get mine to load though (well, it loads but then crashes)
All the Game + Watch galleries are fun, if you like that kind of thing.
the old Tennis game is STILL very addictive!
and of course Tetris, the original B/W is still my favorite. It would be amazing (unbelievable) to get internet play with this! I'd be shocked.
Klustar - another dumb, simple, very addictive (puzzle) game, you must try it!
Konami made original Contra, Castlevania, Gradius games for the system too.
Ms Pacman has a bonus game included, the original arcade "super pacman"
RTS fans should check out "Warlocked," that's supposed to be pretty good. there's even a couple of conversions of Heroes of Might and Magic which is a bit long on gfx but also very faithful, considering.
Project S-11 is the last vertical shooter made for the system.