Well M4 GBBR

Externals: it has a nice black, it is not completely flat, but no glossy either, not sure how to explain it. it comes stock with a LE stock, it is a little wobbly but not too bad. the RIS (CQB version) that it comes with stock is a little wobbly as well. the outer barrel is wobbly but can be fixed by tightening the delta ring. the receivers are made out of a nice feeling metal, it is definately NOT pot metal. the receiver (at least on mine) are not completely flush, and have a little wobble.

Internals: the bolt is made of, what feels like, the same metal as the body, the loading nossle is plastic, but has not given me troubles. the buffer tube has a screw on the back (that also holds in the spring) that is adjustable to make the ROF faster of slower. the stock buffer is plastic, so it should be replaced with a metal one (note: the buffer TUBE is metal, the buffer itself is plastic). One of the trigger pins on mine broke so I would suggest replacing them (note:I replaced mine with real steel trigger pins that my buddy gave me and they fit perfectly). the stock bolt catch wears down VERY quickly, after about 250-300 rounds it becomes utterly useless, so I would suggest the G&P steel bolt catch, even though I have not replaced mine yet.

overall it is a very good and solid GBBR (especially for the price) if you don't mind a little wobble and a little upgradeing.
if you have any questions feel free to ask and I will answer as best I can

side note: I would use the GHK mags for WA GBBR, and the one that came with it is pretty crapy