Far, far too big a question to answer here.
There is an overvioew list of the differences betweeen V3.5 and V4.0 here:
http://msdn.microsoft.com/en-us/library/ms171868.aspx[
^] - and it's only an overview!
I suggest that you learn to use Google to find this kind of information for the other versions - the differences are at least as big!