Having cleared the game twice and died at the Wizard of Yendor 3 times, here are some of my thoughts regarding the current game balance.
1) Ranger and Duelist seem to be too similar. They only share 1 skill, but Strafe Attack is simply too good that these two feel like the only difference is how they resolve high priority targets to me. That and the duelist has a slightly rougher start due to starting without a ranged weapon.
2) 2-handed weapons seem... underwhelming. I think part of the reason is that they tend to appear quite late in the game, where defense becomes more important and when you have already started to commit to a build.
3) Of the 5 possible Wizard of Yendor mini-maps in the final stages, Ice seems to be the most difficult. Electric is interesting, in that it has the possibility of instadeath for the unwary player. Physical is also interesting, and it's likely you'll be forced to deviate from your usual strategy. Poison feels like it's somewhere in the middle, and Fire seems to be the easiest.