When coming from the ArcGIS Engine world one of the first things that catches your attention with ArcGIS Runtime for .NET is the fact that you do not need to install it on a client device.
You merely need to include the Runtime files with your application.
This may seem like a small thing but when you are dealing with maintaining software on thousands of client devices it is awesome!!
Not having yet another pre-requisite (and a 500MB+ one at that) really helps deployment.
John Selkirk 