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.
I never played it, and don't particularly care about what people think of either experience.
I didn't say it was the same, but, if someone feels that way, they are entitled to care about different aspects of the single player experience.
People are entitled to be as aggressive as you are, and I find it strange that you would ask others to keep their opinions to themselves, if they found Black Mesa to be the superior experience.