Full disclosure: I was involved in the alpha and beta testing of GreenHAAS. If I hadn't liked it from the beginning, however, I wouldn't bother to write a review.
This plugin is an instant inspiration box for that not-quite-popping track in your session and has quickly become a staple on my vocal tracks. The comic-y UI without numerical values definitely helps you "use your ears" and even with the wildest processing its CPU usage is very light. If you're looking for an "instant smile generator", look no further.