One word kept popping into my mind the longer I played: "dogshit!" There is so much potential fun to be had here, but there are a lot of problems and they're right in your face from the get-go. Firstly, part of the appeal of the first Xeno Tactic (great game!) was that you were fighting aliens, not boring old vehicles. You don't have to steal images from Alien... nobody owns the idea of space monsters, so you can go nuts. The designs for the different levels of creature in the first game were great.
Then you play the first level (NOOB difficulty, mind), and the first thing that happens is some of the enemies get through. You have to choose the first turrets and upgrades you use VERY carefully, or one gets through on the first wave of the first level. That means less money and less health for the remainder of the game. The worst part is that you're still looking at the interface, comparing statistics and effects for the different turrets when the enemies start coming. Even the first wave has a time limit this time! Then you try to place turrets, and oops, the help screen doesn't tell you which turrets can be placed everywhere and which can only be placed on walls.
The main problem is that there are too many choices right away. You have all your turrets at the start, and there are almost unlimited ways to upgrade them (help screen doesn't tell you, but the first upgrade for any turret is almost nothing, and then it gets more potent as you upgrade more). Even though all the enemies fly, you can't hit them with the Sky Beam. Unfortunately, the Sky Beam and a few other turrets can actually MISS... leaving you cursing with rage when the enemy with one tiny block of health gets through, and you wonder why you bothered buying and upgrading the cannon in the first place.
Too many problems to list, but that's the first part of the first level (which I NEVER BEAT). I got to the last level in Xeno Tactic, but this is totally different. For Xeno Tactic 3, I beg you, have a tutorial, don't allow any of the expensive turrets to sometimes miss, have other people TEST the game first, make sure the flying enemies go through the same door, allow us more room to control where the enemies go, and don't have one mistake ruin 20 rounds of progress! I don't want to see Xeno Tactic end like this, so please, think about creating a sequel with a sensible difficulty curve.