I can speak for nobody, but myself.
And for me, the Half-Life series remains one of the most repayable, enjoyable, and well aged traditional linear first person shooters I've ever played.
I love the expertly constructed pacing and level design, wherein every single area and encounter feels hand tailored and unique, the series never regressing to monotonous corridor runs and repetitious encounter grinds. Moving between each room, down paths, and through open areas is a cohesive experience, the line between artificially constructed set pieces and encounters (that all games have) blurred, making it scarily easy to lose myself in the pacing momentum as I progress through the game world.
I love the attention to detail in Valve's art and design, a comfortable blend of grounded realism and true science fiction. Combine wear armour that seems practical and believable. Enslaved mecha-species evoke an image of organic and machine combined. The little nooks and side areas, props and assets placed in such a way that rooms feel previously lived in, and that subtle little stories have taken place around the game world even if you've never experienced them yourself. No location is sterile or empty, despite the linearity.
I love the narrative, even though it's wrought was cheese and literature tackiness. I love the cast, believable enough to drive the story forward but never unnecessarily intrusive on the flow of play. I like Alyx, her commentary sometimes funny, sometimes serious, always enjoyable. Gordon never speaks, and I'm okay with this. I don't need Half-Life to be the forefront of cinematic, interactive story telling. I like that the story treats you as if what you know is generally all Gordon knows. I like that much is left unexplained and left for you to discover, yet at the same time so much extra lore and evidence is poured into the narrative for those willing to stop, look, and listen (see: Breen's Nova Prospekt speech).
I love the gunplay. No, it's not the best around, but I still love it. I like the oomph of the shootgun, never anything less than immeasurable satisfying landing a full blast of pellets into an opponent followed by that chunky "shuck-shick" as you pump another shell into the chamber. Nailing enemies against walls with the crossbow feels great, as do headshots with the revolver. The tremendous rapid fire thumping of the Combine plasma rifle, and it's disintegrating secondary shot. The wild spray-and-pray submachinegun. Guiding rocket launchers past defensive fire of Striders and airships. The series has never strayed from its old school run-and-gun encounter design, and I've always loved those games.
I love the soundtrack. It's so minimalist, rarely intrusive, yet phat in electronic. It's geek sounds. Thumping beats that kick in at just the right moment.
When it all comes down to it, all of the above have given me fonder memories across Half-Life, Half-Life 2, Episode 1, and Episode 2, than any other series to date. No exceptions. Yes, I love them all. Even when people lament Episode 1, I still fucking loved it. Loved it. Each game is packed full of an astounding quantity of set pieces and unforgettable gameplay segments. Every single one. Each never stops delivering on something...fun. And memorable. And interesting. And exciting. And unlike anything else in the series up until that point. There's always something new, no matter how small or large. And this philosophy never let up right until Episode 2's credits rolled. It's the most consistent first person shooter series in the medium.
So why do I want Half-Life 3 so much? Not just because the story left on a cliffhanger, but what Valve does with the series in all elements is still totally unique, fresh, and distinct from what more or less every single other developer is doing. Nothing, nothing plays or is constructed the same way as Half-Life. Nothing other there scratches the same itch, in story, art, pacing, and gameplay. It does its own this, does it so very well, and as it stands the medium has been without what it does for just shy of six years. Questions of stagnation, and milking a franchise are totally irrelevant to me, because I never felt Valve did this with Half-Life. I didn't feel it about Episode 1. And I didn't feel it about Episode 2. Each was as fresh as it needed to be, and so I expect I wouldn't feel it about Episode 3/Half-Life 3. I wan't Valve to make the series I love, in the way they make it, because they're just so fucking good at it.
And I know most of what I've said is subjective, and pretty obnoxious fanboy dribble. But there it is. There's a reason Half-Life is arguably my favourite series in gaming, and why Half-Life 3 is literally my "most anticipated" game (in theory). I recognise it has issues. I recognise not everybody likes the things I like, or to the extent I do. But I don't give a shit. It pleases me immensely and I'm selfishly going to embrace that, and go giddy at the prospect of having more.