Each .NET version is released with some significant improvements:
.NET 1.0 - 2002 Initial version (1st release)
.NET 1.1 - 2003 Update on 1.0, added provider for Oracle
.NET 2.0 - 2005 Generics were introduced.
.NET 3.0 - 2006 WPF, WCF, WF were introduced
.NET3.5 - 2007 LINQ and ADO .NET Entity Framework
.NET 4.0 - 2010 Dynamic support for languages and TPL (dynamic keyword introduced along with Task Parallel library )
.NET 4.5 - 2012 Asynchronous programming support (async and await keyword introduced).