Dream Master ($1.99) by Zarrus is odd and different. Some might find this to be refreshing and new, some might not appreciate the "out there" approach. I personally feel that the style of this tower defense game fits well with the story it offers. So, let me explain that to you.
Think "Donnie Darko" of iPhone games. You play as a bunny though, and you don't have any imaginary friends - or real ones. You are mentally deranged, bloodshot eyed, and repeatedly have horrible, psychedelic nightmares. You run across the Green Guru in one of your dreams and he offers to help you defend yourself from your nightmares hoping to save your sanity. You have no choice, so you accept his guidance.
The whole game is completely hand drawn by what looks like colored pencils. It's a nice effect.
The first nightmare (level) you endure comes from within the Creepy Forest. Like every other tower defense type game, you need to fend off intruders before they reach their desired destination. In this game, you need to stop the nightmare creatures from reaching your brain and feasting off of it.
You are given concentration points (CP) that allow you to purchase weapons (soul suckers, carrot shooters, etc.) to defend your head. You can also speed up the game with fast forward, or use the slow down skill to help in those precious seconds.
A few things I did not appreciate. The game only comes with two levels as of now, and they only have a total of 57 waves. Also, there are only four to five predetermined spots, marked by ying-yangs, where you can put defenses up. In most tower defense games, the player is offered a little more flexibility in this aspect.
This game is limited to the iPhone only and with the the pricetag of $1.99, I'm going to say pass on this one. It's creative, no doubt about that, but it just doesn't offer enough.