This doesn't seem too unreasonable, to be perfectly honest. They're looking for a proven design manager; and while using a meta-critic score isn't exactly an "ideal" way of going about this, it does demonstrate that the person has worked on at least one critically well-received game. It doesn't specify which position the person held when working on the game (well, haven't looked at the actual position description), and presumably this the one requirement which probably has more leeway than others. I'd suggest dropping the minimum meta-critic average to the 75-80 range, it's a bit more reasonable while still setting the bar for a decent game made.
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The other requirements are a bit more cut-and-dry, and nothing too bad.
Six years design experience in games? Fine. Four years management experience (presumably allowing for overlap with the design)? It is a management position in a renowned developper position, they don't want a newbie for it. Three credits on published games? Proof that the games you worked on got made and released, definitely an asset.
And one game with an 85+ meta-critic score? This is probably the best qualification one can have, as it shows you've worked on at least one good game and not three random pieces of whatever. When factored in with the other requirements, it shows that it wasn't a fluke either. Still, that bar is a tad too high; not to mention it's just bad for PR to advertise that sort of thing, the gaming community is not known for nice nor sane. This is the sort of requirement one keeps off the publications, because it will come back to haunt them; after all, Bioshock 2 only has a meta-critic score of 88 on the 360 (kinda too close to that threshold for comfort).
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The other reason they could have put up that requirement is simply to filter out the number of potential applicants. After their first hit with Bioshock, they're probably getting applications out the wazoo; many of them wanting to work on a company which is likely to churn out the next big hit. As such, they're looking for a fast-and-simple way get rid of 90% of those resumes; the meta-critic requirement is both a deterrent to the inexperienced and a way to get rid of those who are clearly unqualified. If someone has worked on a game with a meta-critic score in the 75-85 range and meets (or exceeds) the other requirements, they can certainly apply and hope that the developper allows for some leeway on that requirement; however, those whose best game has only scored a 50 probably could benefit from some more (and better) experience.