Honestly, it IS incredible.
Now I remember HL1 when it has only come out and it was splendid. It looked so detailed back there, so long, filled with puzzles and crazy stuff.
As far as I remember, when HL Opposing Force came out, it was also praised as an awesome and one hell of an Add-on (yeah no freaking DLCs back there). I remember, I was using cheats since HL was hard (and it still is) and I simply couldn't pass through it otherwise.
Now I've finished it honestly with only my skill alone, or should I say.. Survived it. With a constant save/load, trying to stuck as much of the little HP given as possible, using up ALL of the weapons, tools and explosives given, and Honestly, after years of modern shooters with, you know Health Regen, Dumb AI that's standing still and shooting after a huge pause, linear gaming and a hell lot of ammo on round I'm voting for that era of FPS games to be back here.
Forget the graphics I was SO concentrated on the action, simply sucked into game, I really couldn't stop. For the first time in YEARS I have finally had challenge, and if you, my friend is still willing to have challenge in the one genre that puts your reflexes and aim to the test, you HAVE to fight through this game. You can either realize what it trully means an old-school way of making FPS games, or you might remind yourself of that wonderful era, when we were really proud of ourselves to get to the title in the end where you sit there relaxed and realizing it's over. No wonder modern FPS can't possibly make you feel the thrill, they don't have the guts for this.