I think this game gets such a high review rating due to inexperienced PC users voting on their best game at the time.
This was the just about best pc first person shooter in it's day, but certainly not the best any format game.
Goldeneye, particularly, and alao Perfect dark are far superior games as they come out of their boxes. The multi play advantags of On-line and local area network compared with split screen gameplay make up for this to some extent. As a single player game it was some considerable distance behind the n64 front-runners.
Even with the various add-on packages available the PC could not compete with the abovementioned games.
The intelligence, variety of weapons and gadgets, sympathetic graphics, control system (on superb n64 pad) and in particular the number of enemies on screen is much, much better.
Half -life is a follower not a leader. Reliant on loyalty from the then ignorant PC crowd.