While I really enjoyed the concept, and had a lot of fun with it, I'm with Sin-Crow that the difficulty curve jumped exponentially in Abnormal Zone. The huge swarm of suicide bots will wreck whatever you have at that point, which means you'll be scrambling your defenses to catch up.
Waves 7 and 8 are also extremely hard due to the sheer amount of missiles heading your way. Even with anti-missile bocks, anti-air blocks, all shielded, and throwing in what offensive/freezes you can, the flying units will still shred through your defenses faster than you can build them. And not even making sacrifice blocks will help you because they'll occasionally launch a few missiles at your base anyway. And this is all compounded by the fact that you have to defend two separate sides.
Overall, fun experience until Abnormal Zone; when it just hits aggravating and unfun. In my opinion, that level needs to be drastically tuned down as it seems on the level of "Did Not Playtest" difficulty.