Let's me echo just about everything the author is saying:

In theory and practice, the Stoner direct impingement system where gas is vented directly into the receiver requires vastly more maintenance than piston based designs. To my knowledge, no one who isn't accepting large numbers of donated M16s uses this design in their service rifle, with Canada an obvious exception to the rule. Absolutely no one.

It has two advantages that I'm aware of: the front of the rifle is lighter in weight, and has better inherent accuracy since nothing in the front is moving. However the Swiss, who care infinitely more than the US Army about marksmanship, didn't find the latter to be an issue when they developed their own 5.56 NATO rifle. (The Marines still care about marksmanship, but don't have any choice in their service rifle, except in rejecting the M4 and sticking to the 20 inch barreled M16).

5.56 NATO is a lousy round for stopping people, although the exact details were not elucidated until Martin Fackler did the research in the '80s. At low velocity, all things being equal the round just travels straight through, doing one flip to exit backwards (what happens when a bullet changes media like this). If the velocity is high enough, the round breaks at its cannelure (a crimped indentation that mates with the end of the cartridges brass to keep the bullet in place during rough handling and firing of other rounds), creating two pieces. At higher velocities, the back end will fragment. As a rule of thumb, for every inch chopped off the barrel, you loose ~50 yards of effective range due to this mechanism. Which causes one to wonder why the Army switched to the M4, sacrificing ~275.

The answer I see to that is the total, and I mean total, corruption of this part of US Army procurement in the post-WWII era. The Army did OK with the 1903/6 Springfield bolt action rifle (a copy of the 1898 Mauser), and superbly with the M1 Garand semi-auto rifle for WWII and Korea. But after that the procurement process was totally corrupt, as in samples of other designs were physically sabotaged so the M14 could be adopted. It's a Garand with a better gas system and a detachable box magazine, both good improvements, but outside of a good trigger pull it's probably the worst design adopted in that era because it leaves so much of the action unprotected from the elements.

The situation was so bad the Robert Strange McNamara's DoD of Vietnam infamy forced the AR-15 onto the Army, which as mentioned in the article totally screwed up the procurement of it (and one is allowed to suspect sabotaged it by e.g. not properly supporting the cleaning of the rifle). As the author mentioned, a lot of good men died in Vietnam due to unreliable M16s, which, I'll agree with the others, has been kludged to a barely acceptable state. But again, I'd say it's the worst of the currently issued rifles, except perhaps for the Heckler & Koch G36, a rifle that's infamously issued to armies that don't actually it in war.

Continuing with the procurement corruption, what prompted the move to the M4? Uncharitable people like me believe it's likely the fact that Colt lost the M16 contract to Fabrique Nationale d'Herstal (National Factory of Herstal, Belgium), which despite its name and origin has had a tight relationship with Americans and America since at least the '30s. So Colt came up with the propitiatory M4 and lo and behold, the Army switched to it.

Except now Colt has also lost that contract to FNH, and their factory in South Carolina is even more busy (they also at last count provided all the barrels for our machine guns, plus manufacture Winchester and Browning guns; in history, John Moses Browning (PBUH) first worked with Winchester before moving mostly to working with FNH).