There's a lot of stuff that's new and added in .NET 4, but not in that "overwhelming-I-need-to-relearn-everything" way. More in that, "oh, this is way easier/simpler now" way. Like, moving data around with ADO.NET DataServices is easy, binding with client templates is easy, there's F# if you need it, the "dynamic" keyword if you need it, Silverlight's already installed, oh, and the parallel stuff will freak you out, but in a good way.
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