Two things that really hamper this as a dungeon game:
Levels are arranged in the most boring fashion. The hero gate is always RIGHT next to your first treasury, without fail. This significantly reduces your options for dungeon building. Forget all the rooms you can make, their arrangement and place is all secondary to that first intersection where the heroes' choices are "ruin the player" or "not ruin the player."
I've had 1 honest to god good start in Chapter 2. There was about 10 tiles between the gate and the treasury. It was still the first thing on the heroes' path but at least there was space between the first intersection and it. So at the first intersection, I made one path a loop full of traps. About 75% of the time, the heroes walked that path and got killed by them.
The second decent setup in Chapter 2 was only that way because I built a monster den, which when active drew heroes 100% of the time down a long, winding corridor with traps to a room where I could teleport minions to support the Minotaur on the throne. Otherwise...the treasury was the first room they'd hit.
The second major thing cramping this as a dungeon game is, as people have said...zero AI. And that's probably the most disappointing thing. Putting guys on patrol gives the false impression of life and activity...but the fact AI won't eat on its own is what really kind of drags the whole game down. I can see why they probably did it. Anyone who has played DF can. But DKII got around the problem by just letting you grab and teleport people, which usually retasked them. DKII was smart in that it didn't have you waste time and clicks on stuff like this, keeping your attention free for combat. Impire kind of grinds down your attention by requiring you to be constantly vigilant for ladders and food. Food stops being so much of an issue when you get the squad mascots that regenerate aggressiveness. That and keeping them following Baal pretty much ends the feeding game with your squads.
There's several points of inconsistency or poor execution that are really, really irksome. The fact the zoomed in mode is identical to management mode except in what it shows and allows is really annoying. You can command and select unsquaded units from management mode, you simply can't see your selection. You can even order those guys to attack stuff from management mode. Why the hell didn't they bother to include unit highlight in the management mode view? Instead they swap in these giant fucking icons that become impossible to click when guys are bunched up. Icons get hidden under other icons, making you visually lose track of your squads...For example, when ladders show up and I teleport a squad next to them.....they do not immediately attack it. No, I have to click the ACTUAL LADDER OBJECT from the management view to ensure they'll attack it. It even shows up as a tiny green blob under the (totally unclickable!) yellow ladder icon. A tiny green blob that is what your UNITS WOULD LOOK LIKE IF THEY'D DEIGNED TO ALLOW THEM TO BE SEEN FROM THE MANAGEMENT VIEW! And if I teleport the squad too close to the ladder, their icon in management mode and its click box over rides the ladder object. Meaning I have to zoom in to target the ladder. Op, and if I teleported the squad from the Squad menu, I'd better remember to click their icon first before ordering them to attack that ladder, because the squad isn't actually selected. Oh, and clicking on an enemy icon in management mode doesn't actually make the unit attack them, no, you have to click on the ground next to them, even though in zoomed in mode, right clicking on an enemy squad makes your squad attack them just fine.........Gggggrrraaaaaaaaahhhhhhh! Just be fucking consistent, for god's sake!
Some restrictions are over the top in the game, to prevent issues. You can't build within 2 tiles of the edge of the map even though it's marked as digable soil. You can't build rooms next to each other, there's almost always got to be a 1 tile gap between unbuildable stone surrounding each room. And since it's so dark, you often can only barely see the undiggable edges of stuff. Digging corridors is likewise problematic, they often don't want to turn or connect, even though you clearly have the room, some algorithm is like "Nope, sorry, that's too close for me." Sometimes the corridors are misaligned from where you want to connect to, forcing you to dig in twists and turns until it connects in a way that the game is happy with. There's no way to cancel digging or room designations, meaning everything you lay out is permanent. There isn't any way to destroy rooms which means you can never destroy that first, vulnerable treasury. And even if you could, the game would probably interpret that as you losing, since if even ONE Of your treasuries is destroyed, it's game over.
It's like the devs realized that, within the campaign structure, the only way they could really challenge the player was by putting their weaknesses where they had to be constantly defended.
And just within in working gameplay....in a game that's about building units, skilling them up, upgrading their gear, and arranging them in special ways to activate special benefits....Not giving the player any real control in combat just leads to a lot of dead units and a lot of busy work rebuilding squads. Heroes get strong enough later on that 6 vs. 20 + Baal means you're probably going to lose 1 caster or tank. I haven't seen a squad able to win a 1v1 fight with another squad of heroes since the early game without losing someone. That's why I send all my troops to do anything: to respond to ladders and hero invasions and to explore the map. Why take the chance of losing units, especially when you KNOW the other 2 to 3 are sitting in the dungeon doing nothing except getting hungry anyways? The only reason to not take more units is it's slightly less micro to blob around or teleport in 1 or 2 fewer units.
It turns out there is a way to make squads attack specific targets. You can set squads to attack specific marked targets (heroes marked for Extraction, Training or Imprisonment.) I'll never use that, because there's usually enough time to click a few heroes for those marks before they turn into a clusterfuck of highlighted objects and names. There's no way you could do it with precision, and it's yet again more click-holding on a mass of shit that's constantly moving around. Gee, you know what would make this so much easier? A fucking pause button!
The pacing is surely an issue, because I feel like I've spent 4 levels doing things that could have been addressed in 2.
Lastly, it's kind of annoying to me in a building game when I'm not allowed the full use of everything, that I've played mission after mission to use. Crunching the numbers, there are not enough DEC points available to be earned to build all structures, all units and to get every upgrade. There simply isn't, by the end of the game. Which means you have to pick and choose which upgrades you want, which rooms you want, and which units you can live without. Normally I'm ok with "fewer options can result in better gameplay." Not in a dungeon building game though. I want to see the wealth of my realm spread out before me, build the super dungeon, ect...And the fact I find myself grinding DEC points (the only reason I bother to capture heroes anymore, or lay all my traps) just kind of adds insult to injury. I grind and do all this stuff, and I still don't get to have everything.
I don't feel totally burned by the game, not like I did Dungeons. There's a small nugget of sim goodness supported by the visuals and the atmosphere, and a core game that would be fun if it weren't all of the above. The game is still less of a dungeon sim than I thought going in though, knowing that it was more of an RTS. That's ok, those are disappointments I guess I could live with. What's really a problem is the basic things Impire fails to do, to support its own gameplay and the things it actively does to make it tedious, repetitive and annoying to click. If you're a meticulous kind of gamer, Impire will grind you down with the amount you'll be required to do to run at optimum.
I don't remember, did DKII have hero invasions in the campaign mode? Like regular, constant hero invasions? Because both Dungeons and Impire, I've decided one of the most unfun, annoying parts of them both is them throwing missions at you while you're also being invaded by heroes. It makes everything a deadline, clicking as fast as you can and trying to get all your ducks in a row before the next scheduled invasion. And again, I wouldn't be bothered by that even in half if I had a pause button.
I'm going to start referring Impire as a dungeon themed RTS, because I think saying there's anything actually sim about it is disingenuous. Buy it if you want an ok dungeon-themed RTS. If you're not interested in that, with all it implies, stay away. This is not the dungeon sim you are looking for. I will say though that, compared to Dungeons, there's a lot of gameplay and content for $20. Some of it may be due to excessively slow pacing and some redundancy, but there's plenty of meat on the game. I could see MP being a lot better because you're approaching the game on the the terms it was truly designed for. The systems: the resources, the feeding, the squad caps, the control schemes, the DEC point restrictions...all make way more sense in a MP context than they do in a SP one.