Falcon's Eye is a graphics "patch" for Nethack.
FE is probably the coolest graphics patch ever created for Nethack (beating Charhack and Nethack 3.3's graphic stuff wasn't that hard, I guess, but FE does it about zillion times better than any of the earlier attempts). The viewpoint has been changed to isometric 3D view and the characters, rooms and monsters are pre-rendered 3D. The game now also includes cool background music and graphical introduction.
Regrettably, it isn't complete (only a handful of monsters were done), and the 3D view makes exploring some dungeon levels rather difficult. I noticed that in some cases I was looking at the map constantly =( Also, there's one graphic frame per character. At least I would wish the character to turn around and such...
I noticed this is probably the only Nethack version I've played that made my PIII-600's processor load jump through the roof - well, the game worked just fine, nevertheless, and probably works on slower machines too. (Very few roguelikes have "386 or faster; Pentium recommended" in their system requirements =)
Falcon's Eye looks very promising, though. I hope it will one day become much better. It ain't Diablo II what comes to ear- and eye-candy, but has much more gameplay-related depth =)
FE was made by Jaakko Peltonen. The modifications are available under GPL. The game uses SDL, so it runs on both Windows and *NIXes. There's also a Debian package.
Home page, as of writing: http://www.hut.fi/~jtpelto2/nethack.html