Post above is correct that many of the problems w/ M16A1 back in Vietnam days had to do w/ lack of chrome bbls, failure to maintain, failure to teach troops to maintain.
The propellant issue was also critical, for a gun design that even its devotees admit "cr-ps" on itself as it runs. During first deployment of M16s, the DOD used a powder the gun was not designed for. Guess they got a good deal on it.
I do plead guilty to reading a lot, but I try to be critical about what I read.
One thing I read was David Hackworth's account of how he tried the M16 out while it was still fairly new, and concluded it did one thing really well-- jam.
Hackworth was pretty controversial, but he loved the M1 Garand and the BAR (he also served in Korea), and respected the Kalashnikov for what it was, a little sloppy and crude tolerances but very reliable. So his comments regarding weapons weren't too off base.
To be fair, I also read the book about the Ia Drang battle in Viet Nam, where Hal Moore credited the M16 and the Huey pilots with saving the day for the Air Cav.
I would agree the AR makers have fixed a lot of things over 40 years. But see:
The USA’s M4 Carbine Controversy
I do see an awful lot of people with DGI guns, who seem to experience no problems. But I see them on the range and we don't get too many sand storms here. If snow would provide good test conditions we have had plenty of that lately.
My brother was in the 101st Airborne, 1st Gulf War. He has an M4, but his favorite gun, hands down is an M1A with iron sights. For me, the M1A is a sweet shooter, very reliable, but you need a wheelbarrow to roll it around. And for me, it is a little unwieldy to shoot off shoulder, no rest. And the ammo is heavier and at least a little pricier. That's why I'm looking at the M4s. That, and I just like to try something different occasionally.