Warriors of Oon Arcade mode is really fun! I love how the monsters provide a sense of progression as you beat them and unlock more slots.
The biggest problem to me is some of the controls being unintuitive. It would be nice to see a bit more feedback on things like the score and coins and when the game ends. The shop took me some getting used to as well, and I had trouble clicking on an item and then trying unbuy it to no avail, sometimes ending up accidently using it on one of the oons in waiting at the bottom T_T
I also wouldn't mind if the cost of the items ramped up a bit more slowly so i had a bit more freedom before every purchase felt like a life or death decision, but thats a totally a stylistic choice, either way is fine.
Reset button being easy to hit accidentally has been mentioned by others and is an important point.
Overall I thought it was fun, with interesting and clear art and lots of different strategies to try. I'm enjoying it!