Good for a Short Romp
Reasonably fun, though it quickly becomes apparent that the AI isn't that difficult to defeat as long as you make a factory, max upgrade it, and repeat ad nauseum until their wall is dead. I managed to get through the entire campaign with no damage to my wall with this strategy, which the AI really should have had a countermeasure against. Heck, as I write this, I'm two hours into endurance mode and the AI still hasn't managed to get in a single hit on me, which leads me to believe that the AI just isn't anywhere near efficient enough in the placement/upgrading of its units to stand a chance against any decent strategy.
Overall a fun way to kill a bit of time, but I really would have liked a bit more of a challenge out of the game.