I have one of the originals and I consider it what the AR-15/M16 should have been. Easy to maintain, inexpensive to make, durable, reliable, and accurate.
I like being able to shoot it without having to spend half a day cleaning it. No dirty bolt, no dirty carrier. Cleaning in the receiver is really not needed; cleaning the piston takes a couple of minutes.
Plus the bolt rides on rods like the M3 SMG so that the gun won't hang up if some crud (tree stumps, rocks, old tanks, etc.) gets into the receiver. No forward assist or fancy charging handle, just a plain old bolt handle to which a boot heel can be applied.
No spring in the butt, allowing (on the old model) a true folding stock.
The AR-15/M16 may be more accurate (after millions of dollars were spent to make it so) but the AR-18/180 was the better rifle for military use.
Jim