Stock Android is amazing. It's quick, cohesive, intuitive, beautiful, and just a pleasure to use in general. With that said, however, it's missing the key features which set the Note apart from it to begin with.
You see, when TouchWiz first came out on the Galaxy I (one) series of phones, it was a mess. It was a resource hog and had all sorts of annoying things that came along with it. It's gotten better (slighty in some cases) with every new iteration.
We are at a point now where TouchWiz is beginning to finally be what we wanted it to be in the beginning. It's not completely there yet, but I think the step it went with the GN4 is certainly in the right direction with its material design (Android L) influence.
I've spent considerable time -- but not owned -- every flagship Samsung Android device ever since owning the Sammy Moment on Sprint, and when I played around with the GN4 display at Best Buy it was the first time I could really say to myself that I thought the UI was great.