The Aeon series of skins for XBMC are probably the best-looking skins available from the stock repository, and they are certainly the most customisable. The most comprehensively customisable of the series is MQ 5, compatible up to v13.2 (Gotham). It’s got a slick interface with nearly every possible screen customisable to some point. Even the main menu can be rewritten to suit your needs!
Aeon MQ 5 even comes with a “Games” menu powered by the Rom Collection Browser plugin, allowing one to access emulators, Steam, and local games from a single menu like TV shows or films. Add the Advanced Launcher plugin and you can write a custom launcher script for Netflix or Hulu as well!
Rather than extolling the virtues in my lackluster prose, YouTuber Badluck Justice has a great video showing off what is probably the best XBMC skin available. Check it out below.