CMMG's quality is mostly great. Only flaws are the barrel steel isn't quite up to mil-spec (it's still better than the 4140 that 90% of AR manufacturers use), some of their bolt carriers have weak staking, and their bolts are as far from mil-spec as it gets (4 coil extractor spring, blue spring insert, batch HPT and MPI instead of individual, no shot peening). Easy solution, buy a CMMG rifle (with an H or H2 buffer, if it's a carbine) and a full-auto (if legal in your state) LMT bolt carrier group. Sell the CMMG BCG on AR15.com for $120. Or you could buy an LMT or BCM bolt alone, if the CMMG's staking isn't bad, and keep the CMMG bolt as an emergency spare. If you have to use a semi-auto BC, the CMMG one is a better bet, since it has a shrouded firing pin. Problem solved, you've got a gun that's as close to mil-spec as possible without overpaying for a Colt.
Oh, one "problem" you may run into is that CMMG uses the correct F-marked front sight bases on their flat tops. Most companies use the standard unmarked ones on all their rifles. That means that if you buy a commercial spec carry handle (Stag, Bushmaster, etc.), you'll need to crank that thing up by about 1/16" to get it to sight in correctly. A mil-spec carry handle will work fine, though, and most backup sights are mil-spec height, so the F-marked FSB is a good thing. Easiest way to tell what kind of carry handle you have is to measure the height of the "shelf" underneath the rear sight housing. Commercial spec is 0.800", mil-spec is 0.840".