Except that combat is a tiny part of gameplay in PST, and its flaws can be ignored in favour of how well the games does these others parts. Gunplay is a major part of HL2, and there's nothing else that the game does that justifies putting up with its flaws.
I don't think HL2 is "shit", as I reserve this description for much, much worse games*, but I cannot fathom putting it at anything higher than "average". Some nice ideas, some pretty graphics, very, very boring gameplay, and a shower of GotY awards.
* You want shit FPS games? Someone mentioned Corridor 7 in another thread. Fortress of Dr Radiaki. Mission in Asia. Tekwar. MOH: Pacific Assault. In Extremis. Operation Bodycount. Those are shit games. HL2 is nowhere near great, and I wouldn't even call it good, but it is MILES ahead of the POS FPS games that I just listed. Hell I'd still list it ahead of things like Black Ops and Crysis 2.
What's so horrid about Corridor 7? I see it as a Wolf 3D clone that came out too late, which seems more worthy of being called mediocre rather than truly horrifying. I never played the other Wolf clones (like Rise of the Triad or Blake Stone) though. Did it really suck so much when compared to them? Granted, I didn't play it back in the day, I played it in 2001 or something since I had found the box on sale for the equivalent of 3 euro in a local supermarket.
Tekwar, now that was an awkward abortion though.