Relentless. Cash. Grab.

Each "upgrade" makes the game harder and more expensive. It used to be 5 reinforcements and air strikes every 6 hours instead of 1 now. Ads are pervasive and come on automatically every couple of games without giving any rewards. Some games at least gives us the option to watch and earn coins!!
If you still want to continue playing this "grind on or pay up" fest, upgrade the machine gun and laser first as theyre the most useful. Dont bother spending coin on upgrading the higher levels of towers because youll never accumulate enough energy to be able to actually use them during gameplay as the payout for killing creeps is absurdly low.
The game is basically a Kingdom Rush rip-off. Same number of towers with a similar upgrade path. I would much rather pay upfront for a game like Kingdom Rush and have enjoyable, balanced gameplay with the option to spend money to advance more quickly rather than be frustrated into it, as this game relentlessly tries.
Seems like the Devs dont want us to play their game or, have forgotten that we consumers have many other more enjoyable options in the App Store competing for our time and money.
Too bad the Devs greed ruined a game with great potential. It could have been awesome. And, its obvious the freemium model isnt paying off for them and since theyre even having to resort to fake 5 star reviews

Starman6 about Alien Creeps TD, v2.3.1