Nethack 3.6.0 seems to have some modifications:
The Eye of the Aethiopica might need to be worn to obtain its magic resistance (can others confirm this?).
Artifact blast now will now happen when you polymorph
Doors open automatically when you walk into them, if they are unlocked.
New messages showing your pets growing up.
Elbereth does not seem to be quite as reliable.
Early monsters seem to hit a little bit harder.
Plane of Earth: random single square pockets of open space appear.
Major changes to the Plane of Air.
Astral Plane monsters seem to hit harder.
Meditating bosses seem to wake up earlier.
Can't levitate through the Plane of Water anymore! You have to actually swim, or wait in the bubbles.
Much harder to get Magic Cancellation 3. See other pages for details.