I'm one of those neurotic gaming fans. Metal Gear Solid 2 is by far my favorite game from the series, and I completely abhorred MGS3 so much that I nearly smashed the disc after I beat it. It made me feel like Hideo Kojima sold himself out and went mainstream pop with MGS3. I felt like I had just beaten James Bond Goldeneye after I beat Snake Eater. The stupid references to 007 throughout the game just made the horribly contrived plot worse, but the most insulting thing about the game was probably the hack job of a character known as Eva. It was completely unnecessary added dose of sex appeal that Hideo used to probably try to lure a few more adolescent boys into the MGS fanbase.
MGS2, however, had probably the best storyline imaginable in a way. I mean it did something that no other novel, movie, anime, etc. had done before, to my knowledge. It shattered the fourth wall. I'll spoil it if I say anymore.
But I'd say that Metal Gear Solid 1 is the game that made the series. It's a classic, easy to complete and understand, and a must play if you have a PS1 or PS2. Also, the original version is better than the Twin Snakes because it doesn't leave out any important dialogue or trade in the quality of the script for more action.
I played through Metal Gear and Metal Gear 2 recently on Subsistence, and they were pretty fun for NES games. But I would say that the story of Metal Gear didn't really pick up until MGS1.