To be honest, I'm not an achievement hunter. I know a lot of gamers, and none of them are achievement hunters. So I don't see the whole "all people care about is achievements and trophies" argument.
For me, and for the people I know, a game being good is more of a payoff then a game have easy achievements. And if the game is so good that it makes you want to complete it properly, including all the achievements, its because its a great game that I enjoy playing, not so I can go "My gamerscore is higher than your gamerscore".
As for multiplayer and co-op, well yea, that has kind of taken over the gaming world. Ever since CoD4 revolutionised competitive multiplayer, it has become something to put into every game, a box for people to tick when they review whether the game is worth picking up, and to be fair its not entirely crazy.
Because the economy is so bad and games are so expensive, gamers have become a lot more choosey about their gaming purchases, especially with brand new games. And so we have developed into a community with a rule that if a game is only going to last you 12 hours, then its "not worth buying". So games like Call of Duty and Halo and Battlefield get away with making short, 6 hour campaigns so long as the multiplayer is good enough to last. And when reading/watching reviews, the reviewer commenting on the multiplayer of a game being bad, for many people, means that the game is not worth picking up, regardless of whether the story is 6 or 12 or 20 hours long, regardless of whether the story is a rollercoaster of perfection or a slow repetitive drudge.
To give you 2 examples, Spec Ops: The Line was unanimously hailed by the media for its great story, it was advertised well, but reviewers commented on the poor multiplayer, and so the game did not sell well. In contrast Call of Duty: Modern Warfare 3 was reviewed as having a poor single player campaign, but good multiplayer, and so the game sold like hot cakes.
Because story is something people generally go through once, while multiplayer can be played over and over, the general consensus in the gaming community has become that single player is not the most important thing about a game any more. In fact I've actually started hearing reviewers use the phrase "worth a rental" in a review, because the story was good, but the game was not worth buying.