Generics:
With Java generics, you don't actually get any of the execution efficiency that you get with .NET because when you compile a generic class in Java, the compiler takes away the type parameter and substitutes Object everywhere. For instance if you have a Foo class the java compiler generates Byte Code as if it was Foo. This means casting and also boxing/unboxing will have to be done in the "background".
I've been playing with Java/C# for a while now and, in my opinion, the major difference at the language level are, as you pointed, delegates.
