Good concept, poor level design
Lets get into some of the bad first. Overall the game is easy to players with both TD and FPS experience. The way they make it hard to beat a level first attempt is a boss will appear and you do not know which one until you play and it typically comes at the end of a stage, but not always. Some bosses destroy walls and then all the monsters bypass your towers and you lose even though the first 9 rounds were super easy. So you restart, plan your base for the last guy and it is an easy win. A couple levels your champ does 90%+ of the damage making it more FPS and this FPS sucks without the TD part mixed in...
The towers in the game are pretty basic and there are a couple I found that were useless. Difference is aoe, range, damage, attack speed...
You can choose between 4 champs each with their own main weapon and minor perk. I personally like the sniper since he has high crit damage. This is critical on some bosses/creeps with a small section that crits while the rest is basically immune to damage. While your main weapon reloads, you can use a secondary weapon. Switching to the secondary will not stop the reload process. When I found this out toward the end of the game, it made the game pathetically easy. You also get perks with most of them being useless except for the damage ones.
I did find this game semi entertaining so it was not a complete failure. If basically is a cheap FPS and TD game mixed together to create an ok game. I got 10-20 hours out of it.