I think it's been tossed around here before, but it's evident that a lot of changes to the gameplay and story came too little to late for being the last game in the series. There was no need to make it open world with drive-able vehicles, iDroid and all those nonsense. There was no need to have 90:10 gameplay/cutscene ratio either. Stick to the hospital scene styled gameplay, mixed with some resemblance of an open world and you'll get a more fulfilling game. Admittedly, MGS4 was pretty much a great modernization of the series, as much as I don't like the game today.
MGS4 was great in regards to gameplay. The linear sandboxes were made more intricate than MGS3 and the mechanic of moving around, CQC, combat was made much more fluid. And let's not forget that MGS4 is the best looking game of the series.