I love what aeroprecision did here - Aero Precision M4E1 Threaded Assembled Upper Receiver

It's a very thoughtful design, as is common with AeroPrecision. Notably, the dust cover pin is captured nicely, the brass deflector is angled a little more forward, and the forward assist roll pin is actually a screw that goes in from the top. I'm impressed by all the design elements that set it apart from standard milspec upper receivers. It does have standard interface geometry when it comes to the other components: barrel, lower receiver, and charging handle. However, you're stuck with a milspec dust cover because it does not fit Strike Industries polymer dust covers. Overall good design, and kind of a new take on what most of us are already used to.