Lets be serious ...the chances a new player is going to want to play the 2D NES or SNES version is remote (one is called 'Metal Gear'..the next is called 'Metal Gear: Solid Snake' - The next in the series -the first 3D one- is the famous playstation title called 'Metal Gear Solid' or MGS1)
If you can just start with MGS1; The PS1 or twinsnakes the gamecube remake. It's the game most MGS fans of this generation started from.
It references the story of the 2D metal gear & metal gear 2 for new players to the franchise, where Solid snake goes up against Big Boss and comes across another key character. So you will be on the same path as most players. I started with MGS1 on PS when I was 14 and I kept up with the story referencing the SNES games so I'm sure you will be fine.
Then just get HD collection, and play in order of release.
I agree with - ''Well, if you intend to play all the games anyway it would make more sense to follow the release order, otherwise you'll notice the shortcomings of older titles much easier''
....................you can play the original MSX versions on the HD Collection...
.....I didn't say it's difficult to get hold of...I said not everyone would want to play them. Especially people who aren't even into the franchise yet.....
My first and favourite Metal Gear game is MGS3: Snake Eater and I've been hooked ever since. Once you get into it, you never get out.
I personally played MGS3 first, then went back and played all I could with a PS2/PS3 in release order.
...And for the record, I fucking loved MGS4. It may well be my favourite (MGS3 is tough to beat though). I'd recommend having a working knowledge of the series first though.