The new universal app projects do not seem to support many existing NuGet packages. The specific one that I tried was the Azure Mobile Services .NET Backend. One of the packages it depends on is the ASP.NET Identity Core package, which complains that it requires .NET 4.5, but my project targets 4.5.1. I don't see a way to change the .NET version that my app targets. I'm assuming that Universal apps are currently hardcoded to use .NET 4.5.1, but I would expect a NuGet package that uses 4.5 to work with 4.5.1 anyways
It's probably obvious, but I am using Visual Studio 2013 Update 2.