Most of them also feature some kind of upgrade system where you spend whatever currency the game has to increase the strength of your castle door, along with several other fun defenses like boulders to drop and fireballs to throw. Knights Onrush has all of these features and more, providing much needed depth in to the genre.

On top of having a simple endless siege modes, Knights Onrush comes with a campaign mode and twelve castles to defend, each with slightly different durations and enemy types. Speaking of enemy types, included are eleven different enemies each with their own abilities and behaviors. Knights Onrush has the most extensive upgrade system I've seen so far in a castle defense game, and each element of your castle is colorfully drawn and animated.

Your initial castle includes a hook to hang attackers on to have a nearby dragon come eat them, along with a pit of fire to drop invaders in to. The other upgrades come quick, and Knights Onrush seems to be paced well enough that you're always upgrading something or buying a new defense to play with. This comes as a welcome change compared to other castle defense games I've played which just involve lots of waiting through multiple rounds to buy simple upgrades.

The most succinct way I can describe Knights Onrush is castle defense meets Pocket God. The way all of the different defenses are animated really reminds me of the different punishments you can put your Pygmies through. The enemies are varied enough that you need to use different tactics to defeat them, and as you progress through the levels the choices of when to use which defenses add an unexpected layer of strategy to the game.

App Store Link: Knights Onrush, $4.99