My first experience with the M14 (not "M-14") was in 1963, when I was an Army lieutenant. Although the 101st Airborne Division was the first to get them, replacing their M1s fully in late 1961, my unit, charged with atomic weapons training and security, was not issued them until a couple of years later. My initial impression was that it was pretty much an upgraded M1, and I was glad that most of my training with the M1 could also be applied to the M14 - same bolt, trigger housing group, etc. If you could field strip an M1, the M14 procedure was quite familiar.
In 1969, I purchased one of the first semiauto M14 clones, put together by AR Sales as the Mark IV in 1969. Other than the receiver, all the other parts were G.I. There was a delay in getting mine, and when I got after them about it, they gifted my particular rifle with a national match barrel. A friend came into a batch of G.I. fiberglass stocks, and I obtained one to replace the birch stock that was originally on it - less apt to warp.
I found the rifle comfortable to fire, and quite similar to the M1 as far as operation was concerned. It's a very serviceable, reliable and accurate battle rifle, with greater reach than the M16/M4 carbine series. I devoted a chapter of my book
101 Classic Firearms to it. This picture of my rifle was used in the book.
All in all, my impression of the M14 has been quite favorable.
John
(click for larger picture)