I kept playing because I was curious about maxing out the upgrades and which weapons there are. It plays nicely, but it does get tedious at some point, generated maps starts to look the same after a while as well. The enemies are attacking way too slow so there's hardly a challenge. Like you said, it is pretty basic but it could be the start of a nice timewaster.
Btw, even though you're not interested in bugs, there's a major one when you keep exploring the dungeon (when maxed out) that the game at some points gets choppier and choppier, probably because you keep the whole map (and/or all the enemies) in memory while the map is growing and growing?