Also, keep in mind that I'm not panning your game. Just giving feedback to allow you to improve upon it, or even make a new game that people will love.
They will ignore targets that are further along, simply in favor of attacking their current target (well, all of the towers do this). You could add options for "furthest", "strongest", "weakest", "stick to first target", and so on. The achievements, while ok, should, in my opinion, give some kind of bonus to the game itself, but that is negotiable. It just makes me not desire to try for them. Needs a speed control option. Needs the mute button on the menu, not the individual maps. Being able to see future tower types would be preferable. I also notice that some enemies "claim" to be on the ground, but only air type towers can hit them (possible that it's just a missed error). The delay activated BEFORE the tower fires should be changed to activate AFTER the tower fires, to prevent the "mob in range, but tower won't fire yet" issue. There may be other issues that I have forgotten.
Two posts for length: This will probably be my first post for a game. This game falls flat, for me, BECAUSE it has so much potential. It just seems like it wouldn't have taken that much more to make it a really solid game. The issues I have with the game have (at least, mostly) been covered by other posters: Overall tower damage is just too low for the later boards (this could be rectified by adding more levels of tower upgrades or an out-of-map "account" upgrade area, for being able to provide a constant boost to all towers or specific towers). The targeting mechanics come off as a bit stilted. The towers don't target intelligently. This could be dealt with by 1: Towers with just a status effect (armor reduction, and, by the possible removal of damage from the slowing tower) using a "target the target that is furthest along, and give it a status, then move to the next furthest, etc etc" AI. Towers that do damage really fall flat when attacking a high health target.
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