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. You may still be looking at the interface, comparing statistics and effects for the different turrets when the enemies start streaming in. Even the first wave has a time limit this time! You try to place turrets, but oops, the help screen doesn't tell you which turrets can be placed everywhere and which can only be placed on walls. Speaking of which, since you have less money to build your defences and there are pre-existing walls, complex tactics with building walls and mazes of turrets aren't possible here like in the original.
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 are technically flying, 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. One wrong purchase on the wrong level may as well end your game outright, so while I still enjoyed this one, it isn't the same level of quality as the original Xeno Tactic.
The worst part is that you can't play the last three modes unless you go to their website, which no longer exists in a form where you can find this game. Kind of a sad end to the series.