Now combine that with what the GP said about HL1, some A-tier object manipulation and the impressiveness of VR and you have a game that's a lot of fun to play even if you're just along for the ride (in terms of plot). Throw in a decent story arc, hook people with letting them actually make some tough decisions (earth is descending into a dystopia in the time it's set so plenty of opportunities to force the player to choose between a bunch of bad options and feel guilty about whatever they choose) and you have a highly immersive experience.
I don't mean to make it sound trivial, each one of those things is hard to do right and they all have to be done right but it should not be rocket science. Valve just needs a Decent(TM) game using their existing principals. The hard part is going to coping with the constraints of VR without neutering player freedom within the story or botching the VR part.
https://www.metacritic.com/browse/games/score/metascore/all/...
A good analogy in other media would be Citizen Kane (movies), NWA (music), or Akira (japanese animation). Neither of those would garner mass praise if they were released today, but they were first of a kind and paved the way for moving their respective medium forward.
But I think their goal with HL2 wasn’t really to deliver a compelling narrative, any more than the point of a modern Mario title is to give a compelling narrative. It’s a sandbox with a goal condition. (Sort of like Scribblenauts, now that I think of it.)
HL2 had some interesting mostly-environmental exposition intermixed with an extremely lame narrative arc. You are basically just a guy with a gun who spends most of your time in transit. If you swapped places with Barney or a random citizen in an early scene, nothing would have changed. Your character is sterile. The main character was the environments, some of which were very good, but it felt more like a very long "demo" than a game. Everyone expressing surprise at how you are in fact Gordon Freeman and it just doesn't matter at all. You're a lunatic with bullets to spend, plus a couple science fair level physics ramps to complete. Tomb raider, every single one of them, did physics puzzles better, and they didn't have a physics engine!
I think everyone was wowed at the tech at the time and didn't realize just how bad the rest of the experience was. Replaying it, its very easy to feel (compared to replaying Deus Ex or Thief or HL1)
There was no emotive force in HL2. The story become uncompelling. I think they realzied HL3 would fall super flat without some new technology to showcase, because they made the Gordon story so damn boring. (You'll notice in a lot of fanfics, people actually talk, or they aren't about Gordon at all.)