From my experience yea TouchWiz isn't the best. It has its jink here an there, and like the recent app is abit slow but I'll say TouchWiz on the Note 4 is the best TouchWiz has ever been compared to previous Galaxy S series & Note series.
Samsung is claiming it's gunna b even better on Galaxy S6, Lollipop suppose to change TouchWiz, Samsung is talking about removing all its Bloatware, if you want the app back you download from the Galaxy App Store or Google Play Store. I have a feeling that this will be a big change on TouchWiz and performance boot.
But only the future will tell, but I really don't like there idea of this "edge screen" sounds to me it's a gimmick, also think it will b easier to break the screen. But everybody has their own opinions.