Tower defense games (in which you build walls and other semi-static defenses to help you withstand waves of attackers) were pretty much trapped in the Venn diagram between casual gamers and hardcore real-time strategists until PopCap broke down barriers with the much-beloved Plants Vs. Zombies. Indie Uruguayan developer Ironhide Game Studio recently released Kingdom Rush, which feels more traditionally nerdly while still opening the door to casual dorks.

There's a wee narrative to follow (if you like) about troubles coming to your little kingdom that get darker and scarier as you push further into the game. The designers were quite thoughtful in level design and in offering incremental bonuses to your various defenses that feel satisfying and keep players pushing for the next one*. The game is challenging without ever quite becoming frustrating, though players who aren't used to real-time strategy games may want to crank down to the easy difficulty level until getting the hang of the flow of the game.

The sound and graphics are fun and somewhat reminiscent of Castle Crashers, which now that we think of it is sort of a reverse tower defense game (and is well worth seeking out on PSN or Xbox Live). Here's a screen from the final Kingdom Rush battle:

• This is you, fighting.

Check it out, but only if you can afford the time suck.

*We can't decide whether they lose points for giving players the option to earn experience for liking the game on Facebook. It's a free web game, so we're pretty forgiving. Still, getting that last upgrade requires you to abase yourself on FB and Twitter.

The Stranger Testing Department is Rob Lightner and Paul Hughes.