There are currently too many subdungeons that offer no exploration. These subdungeons suck to find, and many of the new ones actually require you to expend resources, something that is completely infeasible if they're discovered late, making them totally worthless under many circumstances. One of the biggest problems is that most subdungeons will have unexplored space when you first enter, so you want to enter them when you're injured so you don't waste tiles. This means that there's a good 80% chance a player is entering a subdungeon critically injured. If there's combat to be had in that subdungeon, it really needs to be unexplored.
Hit-Ball is one of the worst offenders; it really should be unexplored so you can use it to heal yourself. Soko Trolls is also pretty bad, but at least it has a half-decent jackpot. Subdungeons should really be balanced against "Mothers for Happier Dungeoneers", which is 25 tiles of exploration space, a free potion, and a few pieces of gold. If you actually have to work to earn the subdungeon's reward, the reward needs to be considerably higher than that, and if the subdungeon has no exploration space then the reward needs to be much, much higher than that.
The sudden appearance of many no-explore subdungeons has been really annoying.