Either you're overly critical or I just have poor tastes (probably the latter), but with that being said, I agree that a story doesn't necessarily have to be good...it just has to be believable and/or engrossing (and sometimes just a reason to get the player into the setting). I think sometimes we expect too much and look back to the past with rose-tinted glasses...not that these new-fangled games couldn't learn a thing or too from our beloved classics *waves cane around*
Well... I expect that extremely few people will ever admit having poor tastes, and of course, I'm not among them

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I don't think there's anything wrong with having high standards though... we've got photorealistic graphics... why not have top-rate stories in story-based games as well?
If the devs can't do it themselves (and most can't) why not hire an experienced professional?
They hire professional programmers to do the programming, professional actors to do the acting etc. don't they?
The stories desperately need to grow up... The adolescent boy fantasies aren't enough if they want to keep up with a more mature audience.
(interesting observation: the word 'mature' in games in often used to describe situations of extreme violence, sixual content or 'strong' language... that -and like the several words that are censored by this forum- have stopped shocking me or making me giggle since I was in primary school. So I consider most 'mature' content in games particularly immature)
You might argue again, that a script written by a professional scriptwriter, isn't always guaranteed to better than a script written by a game dev.
I'll agree with that, but I expect that the chances of getting a really good story so much better when a pro is involved, that I personally think it's worth the risk.
PS. Since we have established that as an RPG player I have the great quality of being obsessive,

http://www.rpgwatch.com/show/article?articleid=71&ref=0&id=66 (<--- that's it, click it) where the reviewer ignores many of the game's features and pretty much writes a small thesis about storytelling (including setting etc.) providing very good and clear views of its importance and where that particular game got it right.