We have mostly all played Tower Defense games like Plants VS Zombies or DoTA. Kingdom Rush is a game similar in nature but has its own spin on the genre. One thing I really latched on to was the unique art style of the game. Another rad thing it does is allow you to upgrade the kinds of towers you want to use. Many bad guys...
Yeah, I lost an evening to this game a few months back (i.e. pre-Diablo 3) and have to agree. It's a lot of fun. It's also not soft on the strategy, you can mess yourself up badly with the wrong upgrade tapping your cash at the wrong time. WAY FUN!
It really is. I plan on coming back at it when I ever an iPad.