Bought it to enjoy a tower defence game, ended up with an RTS. The campaign becomes repetitive quickly, having to speed-up your economy before a wave big enough can wipe you out. Despite some variety given by the different factions, defence always boils down to the same few ranged units and high walls. I understand why some people like it, but having to always micro-manage the economy, building walls and defences depending where the wave comes from, while at the same time clearing the areas around to have enough space and resources to keep growing is more hustle than fun. The fact that troops consume food, means that you always have to scale your economy in multiple dimensions (food, housing, resources), plus having to trade for gold, while taking care of the monsters around and the waves changing direction.

Overall, I would rather play Stronghold Crusader despite it having no technologies and a relatively smaller selection of units.

It's good. Much harder than I was expecting, but good. I like that there's RNG to the layout of the levels when you start, though it does occasionally lead to scenarios where it would be extremely hard if not impossible to win. I was also expecting less micro management of units going into it, but that's more of a preference, it's not more than many other strategy games.
Opinions may change as I play more, but as of now I'd recommend it.

EDIT: The difficulty scaling is legitimately unfun. There are 6 difficulties, I picked the 2nd, which is normal. As a casual strategy game player since StarCraft came out, I understand how the genre works. Having normal difficulty scale so hard in campaign that I would need to look up guides to get optimal build order, min max everything, and probably need to reroll the map until I get a goldilocks run is not fun. On super hard difficulties, fine, but not normal. You can tell how many people don't enjoy it by the drop off in achievements; my last one only had 16% completion and I haven't played that much. I'll beat the game on the easiest difficulty, then drop it. I was really hoping to replay it a few times at first, but now I've lost interest.
The game has great bones, but asinine design choices ruin the experience. Don't pick it up unless you want to look up guides for sweaty min-maxing gameplay.

Good indie RTS with emphasis on defense and resource management gameplay. Enjoyable gameplay loop that generally doesn't overstay its welcome. The choices throughout the campaign give slightly more variability though most don't seem very impactful, except for the last one which changes the gameplay loop (much needed at that point in the game). The cutscenes were a nice little touch that injected small amounts of humor in the campaign. There is also some mission variety to add some flavor to something that could easily be overly simplified as just defending waves of enemies.

Difficulty was never an issue playing on "Give Me a Challenge" (Easy-Medium difficulty, not the easiest difficulty but not the hardest either). If you're familiar with this genre (coming from someone who's played Warcraft 3, Starcraft, and other strategy/resource management games) difficulty shouldn't prohibit progress. If you're new to the genre this could be on the harder end of the spectrum to start with as snowballing is critical to success so small, early mistakes can largely affect your chances later on.

Towards the end of the game it gets a bit stale as I'd like more unit variety, to use and fight against, and would also think more aspirational units would be a good addition at the end of the tech tree. (Spoiler: Like the Nightmare General playing as the undead. Each faction should have something like this and more than one. )

Overall if you're a fan of these types of games I think this is an easy recommend, especially on sale. It's nice to see more games in this genre get made and hope these devs continue iterating on this formula.