This is a masterpiece. I would have loathed the notion of a remake changing any aspects of the timeless classic that is HL1, but with the relatively minor QoL and gameplay changes this makes, along with some improvements & upgrades to level design, Black Mesa was somehow able to take the timeless classic that is HL1 and make it even better while still staying very true to it's roots--not an easy task to accomplish.
The only thing holding this back currently is poor support for common gamepads like xbox one or ps4. With an upgrade for gamepad support, I would rate this as a must-play, and one of my favorite games of the year.