WAY WAY WAY WAY TOO EASY
I played this on hard expecting a challenge. It was challenging...until around the 10th wave when I got 3 missile launchers to max level and a flamethrower. At that point I just planted around 30 stealth mines near the barn and got 2 more flame throwers and 2 more missile launchers for good measure. Walk away for 10 minutes and come back to learn not a single stealth mine went off and I still had max lives. This game was incredibly easy to beat even on the hardest difficulty setting, all you have to do is set overlapping crop circles that force them to walk back and forth 30 times and you can set all your guys to be constantly attacking. Also the lack of a cap on the number of towers you can have, I could potentially make 50 of the weakest towers maxed out and still win. This game is so easy an 8 year old can play it on the hardest setting and still win.