I played the first three levels. It's a cool idea, but the dificullty is pretty annoying. Easy is to easy, and normal is to hard. The presentation isn't the best I've seen either. It's not bad, and probably worth $1, but I'd have to play more to give a whole review
I just played the demo on normal and I found it to be just the right difficulty. The key is to build your deck so that you end up with the right combo of enemy destruction (fireballs, lightning), units (I found the card that gave you three peasants and an archer elf to be very useful), and healing (centaurs cards give you a unit AND heal some of your guys). Use the fireballs and lightning early, get a lot of guys out there, and let them go at it.
The demo is 6 of the 32 total levels, and I went through it in about half an hour. Later levels might be longer, but at that rate, I'd go through the entire game in roughly three hours. Of course, for the price, that's not necessarily a bad thing. It was fun and seems to be a solid little casual game with a bit of deckbuilding and strategy involved. It's not very deep, but I enjoyed it.