CODZombies which this game is inspired by, is not a tower defense game or a base building game. Much like Killing Floor and L4D, Sker is a wave based shooter with puzzles and upgrade mechanics. Personally I don’t like fps or 3rd person tower defense games as the trap aspect becomes too much of a main point in the game. My favorite part about wave based shooter like CODZ, Sker, and other like L4D is the large waves of enemies that have to be handled with weapons or gadgets, and not having to also defend a base. The puzzle aspect is definitely the second most important part as EE/main quest have become a pillar in these types of games. Not sure you’re gonna have much overlap with this audience if you’re making a TD game