Recently got a whole set of 4, 5, 6, and 7 cubes based in large part by JPerm's end-of-year recommendations, but was unfortunately not particularly impressed with the Yusu 4x4. The out of the box experience is good, but just... good. In comparison, I was very impressed by the 5x5 and 7x7 choices I ended up with so it felt like a letdown by contrast.
Maybe with some more setup, better lube, and breakin I'l appreciate this cube more, but my initial impression is only a little bit better than mediocre.