Creature Defense, with its blend of card collecting and tower defense, was a great idea. It could have benefited from a more thought out execution, but it works fine as is, and can be a lot of fun. And again, really addictive.
Creature Defense mixes up the tried and true tower defense formula by adding cards. For the most part it works, but if you're not already a fan of this style of game you will likely not be won over by this mash-up.