Well, like most of the people, i got into the series in the Solid 1. When i bought the PS1, it came with a demo of a couple of games, including MGS, then, it all begun... I played all the others after this, except for Portable Ops... And i tried, but the controls are just too bad.
The first Metal Gears aren't easy and that's for sure(well, the first one is kind of easy... But the second is hard for them both) and they are good games(specially Metal Gear 2, which is awesome), so everyone should give it a try. I never played the nes versions and i think i'm lucky for that.
And it's not a classic game, but i have to say that Metal Gear ghost babel for GBC(Solid in the us) is DAMN GOOD. It's one of my favorite MGS games. I highly recommend this one.