Himuro, Peace Walker is the sexiest MGS stealth rpg ever. 20-30 hours of pure stealthing in the jungle with good items and variable difficulty challenges.
spoiler (click to show/hide)
it's the story that kind of sucks
It sort of makes up for MGS4...sorta.
I think MGS2, MGS3, and MGS4 stealth mechanics are better than Peace Walker. Like you say, Peace Walker is pure stealth (outside of the terrible bosses) but it doesn't have a lot of the smaller details from the other games. You're not hiding bodies, shooting out radios, and things like that. While it makes sense because it's a portable game to be played in short bursts, it's not as satisfying as those other games. I still want MGS4 acts 1 and 2 as a whole game, or just VR missions.
Someone mentioned Deus Ex HR and that's a good recent stealth game.