Temple of Elemental Evil. I finally finished clearing the moathouse, after several restarts. Some fights got really frustrating but combat was still fun. Everything else in the game, other than the combat was meh. I just started Nulb and I hope it's not as boring as Hommlet. *sigh* If only I could skip all the non-combat parts...
It's the opposite of PST for me, where I wanted to skip most of the combat parts, and everything else was done very well.