Only going to list the main series. (From worst to best)
-Metal Gear Solid V: Ground Zeroes
It's on the bottom for being by far the shortest in the series. The gameplay is pretty top notch (although rather repetitive) but it's missing the plot and story progression that makes MGS so much fun in the place (and well doesn't supplement it with anything else). All of that is really because it's a prologue to Phantom Pain.
-Metal Gear Solid 2: Sons of Liberty
Sorry Wright. There's a lot to like about this game, namely the improved gameplay from MGS1, the music, graphics (pretty damn good for 2001) and the plot is also pretty interesting. But I can't shake the feeling that the game just feels unfinished, namely the latter part of the game and it's reflected in the pacing of the story. Also I thought the bosses for the most part weren't too great. Still all in all, a great game but it has some glaring issues.
-Metal Gear Solid
Out of all of them, the gameplay in this one is definitely the weakest. My first time playing it, it took some time to adjust to the clunky controls and movement. But there are a lot of things which I really like about MGS1, namely the plot and the atmosphere (excellent OST too). I find myself coming back to MGS1 a lot despite it's flaws, there's just something about it that I loved from the moment I first played it.
- Metal Gear Solid 4: Guns of the Patriots
This one is a blast to play, the gameplay is really solid (the best in the series thus far I think) and you have so many custiomization options for your guns. The locations are great, graphics still hold up really well, music is excellent and all the locations you visit are memorable (well most of them at least), and some of the best boss fights int he series. The main reason why this isn't my top pick is the series baggage. Having to tie up this entire series with one game is a massive challenge and as a result the plot is overbearing, confusing and downright ridiculous at times. It's a blemish on an otherwise amazing game.
- Metal Gear Solid 3: Snake Eater
Top of the list and one of my favourite games ever. Tight gameplay (along with moving MGS into the world of free cam), great music and good graphics. The environments were much more open compared to the claustrophobic environments of Shadow Moses and The Big Shell which was refreshing, it also feels like you have a lot more options available because of the environment (along with some new gagets). I also liked how you started in the jungle and had to make your way through to the base and survive along the way, it was a nice touch. Along with that, there were a range of environments from the jungle to the mountains and urban environments which kept things fresh. The story was very campy but also managed to have some emotional moments too and the cast was the best in the series, I really loved using the codec in this game. The bosses too, they were all very unique and just fun to fight I would say overall the best in the series. Definitely a game I will be coming back to for a long time.
Not sure how much sense my late night ramblings made but I really like MGS3.