Metal Gear couldn't possibly work as a movie; It suffers from an advanced from of [and hitherto unknown form of] Lord of the Rings syndrome [meaning there's just too much story there to deal with]
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There is a way to make it work though and it could result in more cash for those who make it. Not one but several animated series. One series about Big Boss and the formation of The Patriots. One Series about Solid Snake [MG - NES up until about MGS I think]. A third, post-S-Snake storyline as seems to be implied by the continued existence of Raiden [or so I Assume: I haven't yet managed to get through MGS4 quite yet]
With all of the given content in a single Metal Gear title, you could probably even make mini-series out of the supporting cast. Detailed descriptions of the humble beginnings of the Beauty and the Beast corps. The early lives of Vamp, 'Revolver' Ocelot, Raven, GREY FOX, Sniper Wolf [and her love affair with Otakon] and, many MANY others.
It would be a huge commitment though and could possibly end up being a longer story than Dragon Ball through GT but, I am sure there are many people who would say it would all be worth it.