What does long mean, for me, it depends on the genre. Sports games have no length (I must have played PES 6 for over 150 hours last year), RPGs have to be at least 30 hours long (at the very shortest). For the rest, 10 hours is fine, 15 good (inc replayability). If a game has multiplayer, than it can have a shorter play through time, because in many cases it is just training for online.
With MGS4, I think MGO will be bundled, but I think that it still has to be 10 hours through to be classified as having a decent length, but for long, I would assume he would have to mean 15-20 hours

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