Didn't like it. Too simple and repetitive. I'd say it's very tough to finish a level without getting almost all the upgrades. Like others have said it's good that there are diffrent routes, but it only helped a little. The armour upgrade only seemed to exist to increase repetition as well. It's not a good feeling when you are doing well and then your engine gets destroyed just because the upgrade is required.
Great game. I was so delighted when I found out that a new Kingdom Rush was released. I was maybe a bit disappointed that it didn't feel as tightly balanced as the original. Nevertheless, I enjoyed it thoroughly.