Decent
I really love defense-style games and this one has truly stunning grafics and animations. And its really fun to play and I got to the third maze. But there are some problems that make the game less fun as others:
It gets too hard too fast. I just managed the second level with selling all turrets I have and building only air turrets to be able to manage the forelast wave of flying enemies. The flying ships are a real pain in the ass, because they fly from top to bottom, thus having a much shorter way to damage your shield. Especially with the turbo special they are just too fast to kill a reasonable amount. You have to build this green special remover for 100 bucks. At best two of them, but the money is rare and then you lack bucks for killing enough ground vehicles. Its a circle of death.
That leads me to the second problem which is bound to the first one. The upgrades are too weak.
The essence of tower defense games is, that you get to some point of domination sooner or later (mostly with a high number of splash damage towers) and thats exactly the fun, that tower defense games cause. You never reach that point in Xeno Tactic II. I would love to see that sooner or later. I have some suggestions to improve this good game:
1) Strengthen the upgrades
2) Make the flying enemies fly from left to right
3) Make the rocket launchers shoot into the air
4) Make the air turrets not miss targets anymore
5) Make walls sellable for fullprice. That prevents from failing a level totally when you could create a new, more effective pathway