No annoying ads. Just one simple ad when starting the game up. There are resources you can buy, but like any good game you don’t NEED them to win. In fact, you don’t need to to even buy them. By playing the other game modes, you can grind out the resources needed. It’s not too challenging of a game, but it does make you think a little. The fact that’s it’s a free game as well boosts it’s rating in my opinion. Great quality, no cost. I honestly recommend buying a pack of resources just solely to support the devs, because we need more developers who make games like this.
Only issues: the recharge mechanic is a bit annoying. But I never found it too problematic.
The slow tower is severely under powered and useless. It should act as an AOE attack, unless the player targets an enemy, in which it will double the slowness at the cost of the AOE.
One more suggestion: The rockets and flame towers also should be able to hit more than one enemy. Their dps is slow enough to make the current tower that hits multiple foes redundant.