Enjoyable game.
I enjoyed the game overall, I only tried the easiest mode, but I beat it without losing a single person. ;p
The only thing that really deterred me from trying the harder modes was selecting your spells. Being able to scroll through them was helpful, but it was damn annoying when I landed on Teleport instead of Fireball and had to wait for that to finish before I could attack, and by then the Demon I was about to kill is unfrozen, and I have to try and freeze him again now. :|
Maybe you could have made the Down Arrow the Teleport activation? Seeing as how I didn't bother using it at all, considering I only got hit a grand total of 4 or 5 times.
I'd have to agree with some others about spell upgrades, I was pretty disappointed how weak full Ice was, I expected some kind of increase in freeze length or somesuch.
I was also a little disappointed in the lack of the walking demons, I think I only encountered two the entire time.
In any case, I found upgrading my Crossbowmen ASAP the most useful thing to do, as it gave the Demons something else to try and attack instead of the houses, and when the city starts expanding too far to walk, definitely throw some levels into Teleport.
All in all, an enjoyable game, 4/5 on the Pico Scale.