I always found it surprising that Java implemented method overloading, but not operator overloading for arithmetic/logical operators. It's such a useful feature for a lot of types and really cleans up code, and the only real reason it's hard to do is because it relies on method overloading. But once you have that, why not just sugar "a + b" into "a.__add(b)" (or whatever).

You don't have to go all C++ insane with it and allow overloading of everything, but just being able to do arithmetic with non-primitive types would be very nice.