One other point worth mentioning: the original version of MGS3 had fixed camera angles. That was frustrating as heck in open-air forests and jungles -- the Subsistence version, released in 2005 or thereabouts, fixed this with true 3D perspective, but I think this (plus the complex controls) cut into MGS3 sales.
MGS4's controls, by contrast, are a pitch-perfect delight -- you can jump into the game instantly and start having fun, which I'm sure boosted sales.







