Guardians of the Galaxy had a number of great points, but one of the things that we all noticed from the very first trailer was the fully lived-in universe it created. Concept artist Kev Jenkins provided designs for Morag, Xandar and Knowhere. They're beautiful.
There's a lot more on his website, where Jenkins describes the process of creating these places:
I designed the Knowhere Robot Head and have included the image chosen by Marvel that inspired the direction. I also Designed and worked on the Zbrush sculpt that VFX used in their DMP's using an initial sculpt I did for the concept paintings. After seven months in pre-production I then hired a team and spent three months creating all the concept assets under my direction while I provided lighting studies for VFX to follow.