I think, that current OS X (Yosemite) style has some problems. IMHO, to make panel and dock transparent is a good idea, but application style looks a little bit ugly. I think, they lost their good old elegance. In KDE5 both panel, widgets and windows are in the same flat style and looks good. Now I changed my mind and I think, that KDE5 looks better than KDE4 and, even, better than OS X.

Good news! But I think, that KDE >=4.10 design is better than KDE5's one. IMHO, it's too bright and flat.