I played the Keeper mode. I liked the game. I won on hard once, then tried to repeat the build to make screenshots and died in the end (one enemy swordsman was too strong, he is right here at my front door in the screenshot)
My impressions after playing.You always have choices: what to build first, how to spend mana (learning vs monster spawning). This is great. Unlike DF, where I was always building basically the same fortress with minor variations, here I have to choose what's the next thing to do (taking into account available resources, your minions, and what is already built). It would be great if the map could force you to make certain decisions. (Say, there is a human cemetary nearby, and you benefit from going into Necromancy early on).
I notice that I delay building the Library, first building the lobby, then the storage room, and only then the library. Probably, it costs me later on.
The game flow is very natural and intuitive. You gain resources, knowledge, minions. The development if the dungeon is smooth. Other things are balanced well too. I was usually going for golems (a few stone, a lot of iron, then lava in the late game), and necro (mummies, and later vampires, when I played second time). To support my army, I had ~ 4-5 gnomes and goblins (They both work at the laboratories and the workshops, right?). Golems cannot pick up items when controlled directly, but humanoids can.
I neglected the spellcasting branch. But I was spawning flies frequently to distract enemies from my real army. You can make a lot of flies, and they seem to be useful.
Sending minions to kill civilians and animals is fun, even a single vampire can do a lot, if there is no military units (when the the village is defeated it seems to be the case). The raven is good early in the game to quickly explore the map at ~0 cost.
It seems that for building the dungeon, you need a fixed amount of resources, so you don't really need more than you are given. It would be fun to make a map with more than one mountain. So, you could conquer a nearby village and move to a better and bigger mountain. All games unfold according to the same scenario. Some, even minor, variability will make the game more fun. Random events, maybe. It can be interesting to generate maps that dictate certain decisions and events (for both, the player and AI).
Controlling a group of units is not very convenient. When you return to the Keeper-mode, you cannot select the same group easily. You cannot control two groups. (You can use yellow flags, but it's not the same). Anyway, this is a minor issue. Also, in the unit-controlling mode, movement is a bit sluggish. Probably it's unavoidable, all the mobs must do their moves, but this delay is not a great thing. Maybe, you can try to do some "shortcuts", for example, doing expensive computation like the Field of sight of the mobs not at every turn, but once in a while, especially for those mobs that are far from your minions and are not fighting. For melee fighters, when they are in combat, their perception radius also can be reduced. Some "shortcuts" with pathfinding also, probably, can be done. Not sure if anything of the above is applicable, but just my two cents. Maybe, you find it useful.
Hints at the bottom help a lot. I could understand the game without reading anything. (I don't enjoy reading readmes). I still don't see the purpose of the treasury room though. For buying stuff? For sidetracking greedy heroes? Also, if I want to read about the types of minions (what's the difference between a mummy and a vampire?), where can I do that? Do they have special abilities?
Overall, KeeperRL is a very fun and well-balanced game. Definitely worth playing. Very enjoyable, though sometimes seems to be too fast for my taste. There is an obvious potential for becoming even better. If I can suggest some ideas for the future development, IMHO, the game can benefit from additional random events and map features that affect your strategic decisions (and AI's decisions as well).
