It's all just so...beautiful. Where most game artists have a palette that starts at "violent" and ends at "dark", Theo Prins' work here has a warmth and colour to it that's as refreshing as it is a pleasure to look at.
Theo works at Guild Wars 2 developers ArenaNet, on whose site you can read a great interview with him where he discusses his style and influences.
If you like his stuff, there's more of it to see on his personal site (including painstakingly-sliced stereoscopic versions of his images, if you like the 3D stuff).
To see the larger pics in all their glory (or, if they're big enough, so you can save them as wallpaper), right-click on them below and select "open in new tab".