I have a Colt M4 tactical and despite all the hate out there, I like mine. It's accurate and reliable. Now...the 30 round mages are too long the bolt release is ornamental and the fire selector switch needs to rotate 180 degrees to the fire position (where full auto lives on a class III) so that's odd and slightly awkward. It also offers metal upper and lower, which I greatly prefer to plastic and the use of pot metal inside the Colt M4 Tactical offends me a lot less than plastic receivers. In the M4 it's use offends many but it's actually solid engineering for the application.
I also have a CMMG dedicated upper on an M4gery lower. With the proper accessories you'll get a functional Bolt hold open and bolt release along with a functional forward assist. It's also accurate and reliable and the weight and balance is close to the real deal. The design of the bolt and barrel allows you to go slightly shorter and get closer to the actual M4 14.7" external barrel length rather than the usual required 16" barrel length as the dedicated barrel extends inside the receiver and takes up another inch or so. If you want to get the most in terms of operating controls that mimic the M16/M4, then that's the way to go.
Best of all it's not and underweight plastic upper or plastic lower receiver weapon. I don't understand why people buy those...