What does a good programming language have?

I'm thinking about making my own someday. What would you want it to do?

>>3
Can I read documentation at the REPL?
Documentation is not code. man pages exist for that purpose, and they do a very pretty job of it.

Can I use a standardized tool to download and install libraries I need?
The package manager.

>>7
Algebraic data types
What?

Several sort of polymorphism (not only OO)
Operator overloading
Garbage!

Half arsed Unicode
Perhaps you should use Go.