This is a classic tower defense game that copies significant features from Defense Grid: The Awakening. There are numerous uncanny similarities. That being said, there are many worse formulas to copy than Defense Grid, and I highly recommend this game as well as an excellent entry in the Tower Defense genre (but play Defense Grid first). It doesn't do a lot to differentiate itself, but it executes well on the basic Tower Defense tropes... tower building and placement, tower synergies, etc.
The campaign is relatively short, but there are numerous ways to replay the same levels giving it longer legs than it would otherwise have.
It is a solid tower defense game that deserves attention. That being said, if you're only going to play one Tower Defense game, it should still be Defense Grid.