Difficult to put into words really. For me, coming from a polygon modelling background it took me some time to realise it's not really about tweaking vertices, edges and faces but more about working with shapes, curves, etc. I also find it a tad annoying that when selecting various components like an edge or a face, I am immediately put into a "tool" or "command". For example, when selecting a face it's the offset tool. I do like working with shortcuts and would prefer to press a key to enter a command. Saying that, Plasticity is pretty amazing. Oh, took me ages to work out I could delete a face :D