When I went back and replayed all the games before MGS4 my opinion of MGS2 went down a lot. I thought it was awesome crazy mind fuck game at the time and I loved that scissors stuff and naked raiden, but while I'm still fine with the story I guess, the gameplay/mission design is pretty lacking for a lot of the Shell. There's a bunch of tedious shit like the bomb defusing, emma escort water stuff, backtracking everywhere and a lot of the boss fights sucked. It's just not all that much fun to play on the Big Shell. MGS1 still holds up amazingly well and is a total joy to run through any time, the level design and pacing is perfect along with lots of great boss fights and an enjoyable story, and then MGS3 Subsistence is still the best damn thing Kojima ever lucked out in making and pretty much a perfect game in gameplay & story. But 2 is kind of eh, ok. 4 is a movie you watch once and then realize how dumb it all was, and Peace Walker is a fun little repetitive portable game, and MGS5 is a sublime playing, unfinished game that has the worst story in the series, and that's in a series where there is Peace Walker.
If I ever gave the series another run through I'd probably just replay MGS1 & MGS3 and call it a day. But MGS2 was worth playing once, MGS4 worth watching once, and Peace Walker/MGS5 worth playing without watching once.