Duke is my favorite Genesis album. I think overall, I like the five-piece band, but while I don't consider any of it "farting around", I think I know what you mean. There was definitely a lot more experimentation, and with experimentation thiings can be hit or miss. It's the misses the bring things down a bit overall. The three-piece band, and even the four-piece, were very consistent IMO. Duke for me is the best of both worlds. Solid, concise, but also kinda proggy and not blatantly poppy either.