Not bad. It's playable, the combat is interesting and balancing between doing the job and dealing with the other monster is good. It's a typical fighting game, and the upgrades give you something to go for.
I had some initial difficulty figuring out what I was supposed to be doing and it took a couple tries to figure out that I was supposed to knock down the building then defeat all enemy monsters.
The upgrades are pretty bland. They amount to stat upgrades. While stat boosts are nice, after a few plays of the game, I don't see how the stat boosts actually change how I play the game. You're still doing essentially the same thing: knock down a building, fight a monster. In that sense, other than serving as a carrot, the upgrades don't add anything to the experience. However, they do feel thematic.
This is a mostly conventional fighting game, which is fine.