Recently heard about UnNethack. I was curious what the difference is really from regular Nethack. Is it any good? Are the differences major or subtle? Anyone think it's better than regular Nethack? Is it much harder?
You can just try it out on our North American or European public server:
http://un.nethack.nu/ 
I like to claim that in general it isn't much harder. There are some things that are changed that makes it more difficult like Elbereth doesn't work Quest Nemesis or high level unique demons like Asmodeus, etc. but those are mostly things that one would have expected to be in vanilla already.
In a nutshell I would describe UnNetHack as "how NetHack would look like if the DevTeam didn't stop developing it". Although the DevTeam already slowed down development some versions earlier than with 3.4.
Some of the changes are: autoexploring, HTML dumplogs, more variants of special levels (e.g. castle, knox, medusa, sokoban, etc.), a separate real ncurses GUI, plus all of the mentioned UI changes from below.
p.s. What are some good nethack patches that are relatively subtle? Nothing with huge major changes that is. More like improvements and sound, effects, ui changes, extra colors. Things like that.
The statuscolors (colored status line), menucolors (color in inventory, spell menu, etc.) and dump character are already standard in any variant.
Pickup thrown, quiver fired ammunition, paranoid (warn about doing some really stupid stuff), dungeon map overview (automatic note taking of dungeon features), while helpless (more info why your character died while being helpless) and DYWYPISI (in the dump, mark any item so you can see if they were identified or not).
Those are also all in UnNetHack but you can download those patches from the NetHack Patch Database at
http://bilious.alt.org/ (although some of the improvements made to them in UnNetHack are of course not in the original patches
)
