The painting of this game as "reverse tower defense" demonstrates an utter lack of understanding firstly of what tower defense means, and secondly, of the long and storied history of Qix and it's many many clones.
Make no mistake, this game has nothing to do with the tower defense genre, and everything to do with being a shameless re-imagining of the classic 8-bit game Qix. That sounds like it would be a bad thing, but the truth is that Qix was a rad game when it released in 1981, and Fortix 2 truly feels like what would happen if the developers of Qix had time-traveled 30 years into the future at the start of development.
Qix featured a simple mechanic, slickly implemented, with a presentation that was unremarkable but serviceable for its day. The exact same thing is true for Fortix 2. This is not a complicated game, but it is a great implementation of a simple mechanic. The difficulty curve is pitch-perfect, making finishing a level without losing any lives achievable but challenging.
Fortix 2 isn't going to blow anyone away, but it does an excellent job of filling that spot in your Steam library for a game that doesn't ask for much in the way of investment, and can be consumed in 5-minute increments while still feeling rewarding, and for $2 or less, you can't really ask for more.