So, I've been playing this game since the 1st release of book 1, like 4 years ago. Obviously, I'm a fan, I like the plot and the unique combat. 

That being said, outside of some personal adjustments I'd prefer to the harem,  there are some combat balance adjustments that might be implemented:

The Winter King is effective at fire magic, and reasonably so at lightning, but ice pretty well sucks. Early game, pure damage is generally better, late game, fire kicks ice's ass. Shouldn't the winter king be really strong with ice?

2nd, experience earned versus difficulty.  The Ace difficulty pays less than king, and the hellion caption (a jack) pays better than everything except chort knight, chort lord, and deep dweller lord. Growing up playing RPG's, there was always a general rule of balance,  and the more effort to win, the better the payout.

3rd, I don't really get the difficulty rankings anyway. A fire deep dweller takes way longer to kill than a poison or ice one, for example, because fire is effective on the other 2. And a Jack steel Guardian is way harder than a Jack demon prince.

Anyway, just some suggestions.