I've played all of the core series.
MGS2- I really loved it. Didn't even mind the Raiden switch, but the story went off the rails and got WAY to esoteric for my tastes. Oh its a simulation? sure, whatever. It was like a beautiful gymnastics routine, which could have been a 10, but they didn't stick the landing. They fell flat on their face with that last hour of fission mailed, corrupted colonel AI madness. WTF
Snake eater- I have the utmost respect for this game, but I don't like it that much. The whole jame's bond espionage cold war era vibe is very cool. I just didn't like healing myself and the wide open environment just wasn't for my specific taste. I like one single base like MGS2 and Shadow moses. I will say that the fight with The End was my favorite moment of any MGS game.
Guns of the patriots- LOTS of fun. I really like this game and all the little call backs like going back to shadow moses was awesome. my only nitpick is the london sneaking part. Besides that, it was awesome.
MGSV- sorry for anyone that loves it, but I hate it. Doesn't even feel like a metal gear game to me and I got bored like an hour into africa and stopped playing. There is no story and it just feels like the whole game meanders. When I play a metal gear game I like to feel like am watching a movie. Phantom pain is just a lot of wandering in the desert and I refuse to listen to hours of audio tapes to know whats up. And spoilers, its all one big fucking bait and switch. Fuck that. And I much prefer david hayter. Rant over
Ultimately, Metal gear solid is still my favorite since it felt like the all around most perfect (for me at least) and it really knocked me on my ass with all it had to offer. Going forward I was expecting the cool next level stuff, if that makes any sense.