One of the problems I've found with AAA product development is that basically what they mean is, big budget for the developer, and hence as high quality as they can afford. When EA turn round and say they're delivering a AAA experience, you can be damn sure it'll have a bigger budget that this Rambo game.
As for scripted shooters being easy to make, relitively true, the main problem with large teams is lack of insight, and direction from whoever is in charge usually coupled with CEO's contradicting the requirements of some director. Alot of pee'in in the wind if you would.
So what's the main reason teams screw up ultra scripted shooters? Because it is in my opinion the wrong way to develop anything, especially a shooter. The only reason CoD gets away with it is because they batter the crap out of the player, and punish them to the high hells if they walk of the designer dictated path, if that path isn't intuitively
"ultra scripted" anything is crap, it just doesn't work, its why as much as I don't particularly like Halo, its certainly far superior to CoD as a piece of software, and I think in turn as an experience.