I finished this around a day ago and really had a great time playing it, much more then I thought I would. I agree with most of the praise AND the complaints about it. The game looks great, I never really noticed any of the changes to the levels (but it's been 5+ years since I've replayed the original), and I liked the homage voice acting after initially kind of disliking it. At the same time though the quick-charge vorts, crazy aimbot guards, and lower jumping height make certain parts a little annoying. Not bad by any means mind you, just a little annoying. Funnily enough, they made me go back to my old FPS habits of quick saving / quick loading like a madman because I would always think "I can do that without taking as much damage".
Seriously, the team did an amazing job capturing the original Half-Life. I'm actually really excited about it being Green Lit on Steam so I can play back through on a harder difficulty setting. Hopefully they will be able to fix a few of the crashing bugs (crashed on me 4-5 times, but I'm a quicksave whore) and maybe fix the "one soldier sees you, they all know where you are" thing.
Even if they don't, I'm still going to play it again. Well done sirs! I'm actually looking forward to see what they do with Xen. Maybe it won't be so horrible for once?
Also, I hope that Opposing Force mod is half as good as this one. I know it's a different team, but a man can hope and pray right?