The first thing everyone says about this App is it lives up to the name! Addictive brings Additive Synthesis to the iPad in a very well thought out package. The ability to morph between patches brings so many layers to your sounds. The inclusion of a unique filter and a mind boggling assortment of modulation options insure that you will lose hours upon hours exploring sound in entirely new ways! See a full review here.
Disclosure: I received my copy for review from VirSyn.