The best mod I've ever played. Sure it's not perfect, I still get lost a lot, and the physics collision of the source engine is somewhat outdated. There is not much real innovation in this game.
But I can feel their passion, they know what HL fans want and learn everything from valve games, HL2's level design, Portal's writing, Alyx's enemy, and of course the Opposing Force elements.
And they actually tell a good and complete HL story, which is much better than Valve.
I wouldn't compare it to other games, but I do enjoy it more than Alyx.