The non-unified type system contradicts the object orientation idea. Even though everything doesn't have to be heap-allocated objects, the programmer should still be allowed to treat primitive types by calling methods on them.
The generic type system implementation with type-erasure is horrible, and throws most students off when they learn about generics for the first in Java: Why do we still have to typecast if the type parameter is already supplied? Yes, they ensured backward-compatibility, but at a rather silly cost.
