S.T.A.L.K.E.R. There, I typed out all the damn periods. No more.
Okay, so here's Stalker: Shadow of Chernobyl. It has a pretty cool story. You're the "Marked One", an amnesiac who just barely survived a big accident on a horrifying truck, and you have only one piece of information: a PDA that says "kill Strelok". Who is that and who am I?
So you do the only sensible thing: wander off completing tasks for the local trader, getting into fights with bandits, mutants, and the Ukrainian military. And for reasons I forget, you decide that the smart thing to do is to try to get to Chernobyl. You know, the site of the world's worst nuclear disaster. Except in this universe it's even worse, with a second disaster causing physics to stop doing what it is supposed to do, creating anomalies in space. Also, a strange device called the Brain Scorcher turns other Stalkers and soldiers into Monolith: aggressive, fanatical, brainwashed soldiers who kill anyone who comes near the plant. And because this chosen course wasn't sufficiently dangerous, you explore various abandoned, or less than entirely abandoned, laboratories which give you (by which I mean me) nightmares.
But along the way the biggest obstacle is the game. Strange bullet mechanics, weapons that wear out and break and cannot be repaired, no matter how much you liked a particular gun, weight limits, and the randomly scattered stashes of valuable artifacts, powerful items created by anomalies, but which are empty until you've found the correct randomly dropped PDA with the location. It's not a pretty game by any means.
In contrast is the third game in the series, a visually stunning and mechanically impressive game, Call of Pripyat. Guns can be upgraded, repaired, and customized to work just as you would want (putting bullets in scary things at various ranges). Stashes exist even if no one has told you the location. The inventory is easier to manage. Artifacts are more fun to acquire, being searched for between emissions (these are a once-a-day Everyone Outside Dies), rather than found purely by chance. On top of all that, there are far fewer loading screens, thanks to most of the outside world taking place in three maps rather than a dozen or so.
But the story...
It can be summed up as this: you're a soldier sent in to look at crashed helicopters and figure out why they crashed. Then you fight some monolith and get airlifted out. That's the main story. Did it sound a little lame? Well yes, it is. There are side-quests, and those add some flavor, but not much depth.
At the time I did not realize this, too busy being scared, or very happy, as I shot mutants and bandits. But after a bit of thought it struck me: Call of Pripyat has a pretty boring main story. Here, I'm going to spoil the big surprise for you, the mystery of the entire game, on why the helicopters crashed. Ready for it? Okay, here it is: the Ukrainian army made maps of the anomalies and the anomalies move after emissions. Wow. Big twist there! No conspiracies, no plots, no secrets to uncover, just "shit moved." Plus some open-ended "something may be going on but we're not going to tell you anything about it" bit concerning mercenaries.
Here's the thing to remember: I had fun playing both games. Sure, the second one had a rather lame story, but it was fun anyway. Does gameplay trump story? Almost certainly, since an unplayable game can never tell its story (which is what SoC was early on, before they fixed most of the really awful bugs). But can gameplay carry a game? Almost certainly, as most PvP can show. And PvE as well, since I doubt most raiders are lore nerds (I mean that affectionately) and most people aren't doing a whole lot of analysis of the quests that they're skimming for quest objectives.
And yet I still wish there were better stories.