In terms of tower defense games, Kingdom Rush is pretty much the dead center standard. It has all that you would look for in a game: endless waves of mobs coming in to attack you, the familiar towers, and a standard difficulty that progresses as you go level to level.
But it is just that. Coming from Armor Games, Kingdom Rush is a little bit too generic. If you are trying out tower defense games for the first time, this game would be perfect for you. But if you just want to try it out, the 174 mb download size is a bit too much. The towers are things you probably have seen before in other games - much as if the developers decided to take the safe path in game design.
And while they do throw in things like achievements, Kingdom Rush is best served as a stepping stone to other tower defense games...like Plants vs Zombies at number 4.