Nice game. I made it to the end but then a JRPG boss killed me.
I think the gameplay is spot on for the most part. The only notable exception is that some enemies don't scale very well if they happen to show up in later rounds. The imp may have a sharp tongue, but he is rather impotent, even on wave 7.
Perhaps the order could remain random, but lock certain enemies to a range of rounds. This may be worth considering if you keep adding new enemies.
Besides that, the post-punch attacks could be explained a little better. I got the hang of them after about 10 minutes which isn't much, but it may still be worth adding some indicator like a flash or something.
Also, consider polishing up the menus, text boxes and such. It seems minor but if you have ever payed an RPG then you know how much time you spend staring at solid color boxes so might as well make them pretty.