Played through the whole game
Most flash games can't keep my attention for long, but I played all the way through this. Difficulty scales very well-- I was often left wondering if I was investing properly for the next level. I found it helpful to skip upgrading, look at the next level's enemies stats/abilities, and then go and upgrade. Helps to know how much to pour into damage (why make your archers do 35 damage when the highest mob at level x only has 33 hp?).
I recognize that this is simply Patapon without a drum, but I still felt it was challenging and very fun.
I look forward to a sequel-- perhaps with a boss? It would also be nice to have control over your other minions, perhaps using the number pad to control everyone (the top three numbers, 7-9, could control ranged, the middle, 4-6 could control melee, and the bottom three numbers, 1-3, could control wizards or something of that nature). In that example, 1,4,7 would be left, 8,5,2 would be halt, and 9,6,3 would be right. I'm not suggesting that you make the player control the attack for each group-- having the player control the attack for just the archers works quit nicely I think, but I think there would be a lot more strategy possible if you could control three separate groups (although some people would find it very difficult, so you could just have an auto-right feature that would make the sequel function just like this one).
I think you would have a pretty hard time having a real boss battle if there was only control over the archers-- they can only back up so much before the flagmen get screwed. By being able to weave the characters in and out of the attack ranges of the enemies, you can keep the game moving better I think.
Also, the heal didn't seem to bring back the temporary fighters (centaurs/humans) just the archers.
If you don't want to make three separately controlled groups, perhaps you could make the range of the arrows adjustable, either through the mouse (which would be tricky, since both hands were already being kept pretty busy with the current control scheme and having so many enemies lagged the game a bit, a horrible situation during mouse aiming), or by having different skills have different trajectories (such as a short range shot that goes almost parallel to the ground, so you can move inside the range of other archers and still attack them. The reason I suggest this is because for a lot of the fights, the elves were basically useless, as they would quickly lose health to the enemy archers, who use the exact same attack arc, and have the added benefit of not needing to move before attacking. So basically, I was forced to zerg several levels with the help of centaurs, which is okay, but kind of boring, as I have no control over them (see a theme?).
In Summary-- the sequel would greatly benefit from either 1) greater control over the movement of troops or 2) greater control over the trajectory of the arrows.
You made an amazing game, congratulations!