I looked at it but was sort of unconvinced, it seems like there's only one or a couple maps and the room based stuff is fairly straightforward? Also no meta progression just new unlocks?
The maps aren't anything to write home about, that's true. There are 3 different maps but I haven't unlocked the later ones yet to see if they do anything, but I don't expect them to be much more than squares really. And there is meta progression, but standard fare, like increased pickup range, movement speed, attack, etc.
The gimmick to the game is the combo/upgrade of your "stands." No fucking clue why they are called stands, but they are the dudes that surround your main dude, and are basically just a different version of "weapons." They don't take damage or get hit, only your center dude does (so turn transparency to like 20% visible otherwise you'll have a hard time dodging properly). Let's say you buy a skeleton as one of them. If you buy another skeleton, you can combine them to make a 2 star skeleton. 2 of those can make a 3 star. OR you buy a skeleton and a wizard, and you can combine those two into an undead mage. Make another undead mage and combine them and now you have a 2 star undead mage. OR you have an undead mage and you build up a 2 star wizard, and you combine those into a lich. Etc. And you have like 7 or so slots around you that you can fill with all these dudes however you want (subject to availability of buying them at the randomized stores of course).
All of that combo stuff is the core draw of the game. None of those are gated behind unlocks, but you don't know what the combos are until you make them one time. Once you've made it you can "target" a specific one (multiple actually) so it tells you which ones you need to buy to make it. So if you target the lich, it is going to keep highlighting skeletons and wizards until you have bought enough of them to combine into the lich. Until you've made the lich once you can't get the targeting help, you are just randomly hoping shit combines into better shit. But once you have done a few of those you start to experiment with your build and combo'ing specific damage types (magic, physical, and pure) so that your synergies boost everyone, etc.
So yeah, you are going to be running around the same few square feet until you earn gold to unlock a door, which just opens into an identical set of square feet so now you can run back and forth between the two, and it isn't very exciting, so if map diversity is a priority, you will probably be disappointed. The draw is combining dudes into stronger and stronger dudes to pair with the other ones you have and making a ridiculous build. And that part is fucking great. Will it be fun a month from now? Maybe not, but neither are any of these games once you've unlocked everything and figured out your favorite builds.