The M4 is just fine in the desert... with proper maintenance... "Based on the AK"... means nothing as far as reliability goes... all it takes are a few minor differences to make a reliable weapon into an unreliable one. I am not saying the Galil is not reliable... just that it was not as reliable as the IDF wanted... Soldiers always prefer the weapons of the enemy.. it is natural... all of our favorite weapons have issues some worse than others...
M1 Garand - the bolt would freeze the the rain... the reason was never really figured out... hence the addition of a roller on the M14.
M14 - uncontrolable in full-auto... whenthere was a real need for a selet-fire rifle.
M16 - not enough stopping power... but the Russian were very impressed with the caliber.. so they designed the 5.45x39mm.
M60 - IMHO total piece of ****... bolt fractures, rivets in the reciever loosing (the fix was to WELD it), too easy to reassemble the trigger group wrong, the gas system has to be wired in place (or it loosens under fire)... the bipod is on the barrel (moronic!)... so you get to carry a bipod with every barrel... and the bipod is too far forward as it hampers raking fire (you have to move the weapon right and left).
AK47 - too short a sight radus, poor trigger, poor ergonomics... takes two hands to change a mag, no bolt hold open device... too short a stock (with body armor)... some of these are corrected in OTHER countries version of the AK.