It's impressive in how many ways they miss the mark of what makes for an enjoyable tower defense game. There's little introduction or explanation to gameplay concepts. For example, the 4th level introduces its first weather effect, except it doesn't really tell you when this is happening, or what its effect is. You have to go out of your way to find such simple things.
You know what other amazing feature it possesses? Enemies drop a cube of additional resources upon death, which you are required to hover your mouse over to collect. Maps become several screens large even from the first level, so if you create a few killzones, you have to constantly cycle between them to scavenge your rewards. It's kind of ludicrous in a terrible way, honestly.
I would best describe Defense Technica as a half-hearted mash-up of Defense Grid (in look, feel, and mechanisms [you quickly acquire what is essentially the orbital laser, towers pop out of the ground in little boxes, etc]) and Kingdom Rush (towers are limited, but gain upgrade paths). Maybe somewhere in there is a kernal of a good idea, but it's not easily accessable, and it's hugely unpolished.
Sadly, this is a purchase I regret.