Anyone who trashes MGS4 is a pure dolt. Seriously, you're daft.
I get not liking a game, particularly the limited amount of actual gameplay in 4, but those that say it ruined anything regarding the story or mythos of the series never seem to actually convince me of what was supposedly "ruined."
Besides, the return to Shadow Moses and the return of Eva are enough to make that game great in my eyes.
OK, I'll bite.
MGS4 was an abomination.
However, it was designed to be stupid.
People didn't just ask for answers to MGS2, they sent death threats to Kojima for making MGS2. People didn't get the meta-narrative(s), they took it at face value and wanted an explanation to all the crazy shit that couldn't possibly be explained.
Kojima got fed up and made a game that reflected his feelings of the current state of MGS.
Making Snake old and decrepit, tired of everything, just doing "One last mission", all because he's obligated to do so. Remind you of someone?
Explaining everything away with horrible explanations that come out of left field (Nano-machines!)? Making Raiden a complete bad ass, ruining his character from MGS2 and making him something the fans would accept.
Connecting MGS3 with the Patriots by having the entire support crew of Operation Snake Eater
become the Patriots? Well people were pissed that MGS3 had nothing to do with any of the other games, have to please those people too!
The whole game was fan service, that's all it was. A game to please the majority of the MGS fanbase who were too "daft" to get MGS2.
Oh, I almost forgot. Eve was retarded in MGS4. Why would she jump into the fire to save Big Boss, even though she knew it wasn't Big Boss? She was with him for all of Snake Eater, she knew which eye was blown off, she had portraits all over the church with the eye patch.