2/5. The difficulty curve is nonexistent. All you have to do is buy the most expensive tower and upgrade it fully. The visuals are good, but nothing else is worth mentioning.
A really easy tactic is to use your meteor at the beginning of battle to hit the opponent's hero. It'll cause him to rush at you, no matter how big your army is.
The gameplay is solid, but the damage calculations completely suck. I did 1 damage for an entire mission, then the next time I tried the first hit did over 20 and killed the guy. Tweak the calculator and you'll have a better game.
Add a feature so you don't have to wait for characters to move into the screen every time. It gets really repetitive having to wait the few seconds, and it adds up quickly.