For me it's mostly the move from an open system to a closed system that makes the later editions less fun.
This section only appeared in the original 1977 edition and quickly vanished thereafter.
"Skills and the Referee: It is impossible for any table of information to cover all aspects of every potential situation, and the above listing is by no means complete in its coverage of the effects of skills. This is where the referee becomes an important part of the game process. The above listing of skills and game effects must necessarily be taken as a guide, and followed, altered, or ignored as the actual situation dictates.
In some game situations, actual die roll results must be concealed from the players, at times allowing them to misconstrue the reasons for their success or failure. In other situations, the referee may feel it necessary to create his own throws and DMs to govern action, and may or may not make such information generally available to the players.
In order to be consistent (and a consistent universe makes the game both fun and interesting), the referee has a responsibility to record the throws and DMs he creates, and to note (perhaps by penciling in) any throws he alters from those given in these books."
A small game with a few rules covering the absolute basics, then telling the referee to make up what they need to in order to cover the universe of shenanigans the PCs will get up to. That's the stuff right there.