Not bad at all
There's actually a tiny little straight-up Patapon game you can find here on NG, but it's dismally short. I've been looking for something like it too, so this hit the spot, more or less. I never had any problem with the beat - since it IS going fairly fast, it's possible to recover from any errors that much faster. Sure it was pretty much lifted from Patapon, but that was obviously intentional and there's nothing else like it online as far as I can tell.
It really needs a menu, where you can customize your army whenever you want (rather than just before starting levels) and see the command list (because if you missed it the first time, you're screwed). The basic spearmen seemed buggy in that they moved backwards when they attacked, so that sometimes they would end up behind the flagbearer, accomplishing nothing.
Also: does the enemy level up at exactly the same rate you do? It seemed that whenever I got a new kind of unit, the enemy would gain it the same level, so that the difficulty remained the same.
A nice little game that I'll probably be replaying occasionally.