Warning: I write walls of text. If you're thinking "tl;dr" at a glance, go with your gut.
Right off the bat, I'll make my point clear. Whenever Valve decides to continuation to the Half Life franchise, I'll be picking it up day 1. I don't care if it takes me a week for Steam's servers to steady out from the load it causes.
That said, I'm in no hurry. At the end of the day, I don't really care much about Half Life's story. When you build a story with cliffhangers that have no forseeable conclusion (Resident Evil movies, EVERY Half Life game to date), you're probably not telling a very good story, and more than likely piecing it together per iteration (see every season of Heroes and Dexter past the first).
Only the story is not really what gets me into that series, anymore than the story being what got me into Prometheus. Half-Life is really a series of amazing moments and sequences, long before it became a standard for FPSs, and, in all honesty, it still does this the best out of most titles. The cinemas never cut to a different perspective and the game RARELY takes control away from the player (even when amazing things are happening). Never mind that the game's biggest events require active and skilled participation from the player, as opposed to the "Theme Park Attraction" approach most modern titles take to this kind of immersion.
Basically, I'll be glad to plunker down and enjoy 6-8 hours of whatever Valve releases in the next few years. Which segways quite nicely into...
Valve Time
So much like this site's titularly loved games producer, Valve has a tendency to release software on the "When it's done" schedule. Franchises disappear for ages, and screenshots have very little value for completion estimates until a street date is on our laps. Even that doesn't always mean a whole lot. And the final single-player games tend to be short (both Portal games, for instance)
I think what most people don't realize about Valve Time, however, and what didn't really click for me until the release and subsequent critical backlash of Quantum Conundrum, is just how much of that results in what we DON'T get to play in their eventual releases. A GREAT deal of every dev cycle for Valve is research, into both how they can extend their engine (hell, look at DOTA 2 and all the Mac/Linux work) and what works best over the course of their games. The chunk we never see is what they find DOESN'T work in their titles, because at best, we get snippets of that in the dev commentary.
Who knows how many OTHER ideas Valve worked on for weeks or months that, as work wrapped up on that segment of a game, turned out to NOT BE FUN. Who knows how many programmer days (e.g. 24 hour periods, not work days) funneled into a gameplay or graphics concept that modern hardware at the time wasn't ready for, and was scrapped (or pushed into future consideration).
Next time you get a chance, if you own a DVD or Blu-Ray copy of Serenity, take a look at the deleted scenes. Most of them are minutes of extra dialogue in various parts of the movie that contributed NOTHING to the plot and actually felt a little "rambly". Half of that movie's brilliance (imho) was what never left the cutting room floor, something that is RARE in video games. "Insert Credit" had a feature on this problem some time ago, and how the rather excessive cost of game development (and this was written before the current console generation started) leads to a distinct lack of editing in games, for both story and level elements.
Basically, look at it this way: Among other things, Valve Time keeps "Scrappy Levels" down to a minimum.