No, what is left is much more than that. You left out the whole gameplay, which to me defines a game.
Invisible brushes, different physics, monsters are different, some attack much quicker and harder, others are dumbed down.
This might feel like an improvement to some people, to me it did not. It does make the GAME a different one though. If only you notice minor changes, don't even mind the different graphics and sounds, then it may very well be a better game to you.
But please do not say it is the same. If you have played Black Mesa, you did not play Half-Life. You played Black Mesa.