MGS4 could be a good game to start with then.
Yes, you'd be spoiling most of the other games' story for you, but it's the only game in the series where you can do a proper Uncharted-esque run. Especially when you get a reward for getting 60 weapons. The only thing I'd worry about is Act 3, as it is strictly stealth (hell, even I don't like that one).
Although, MGS3 has a VERY slow start. Once you're out of the cave is where I'd say it's a fantastic game. I initially hated MGS3 because, like you, I was used to fast paced games like Uncharted. It also didn't help that I started playing it during my Uncharted 3 Multiplayer high.
I just watched some videos on YouTube seeing proper players playing the game and techiing me it's basic mechanics and tactics and I finally became good at it and it became one of my favourite games of all time.
The map had very little variety. In all the other games the progression just seemed to flow a lot nicer… for me at least.
Also, the fact that they had to take out more than 50% of the cutscenes so they could animate Raiden's hair now makes us stare at a green screen of expposition for 15 minutes in order to get the story.
When I say MGS2 is the best, I'm mainly reffering to VR Missions and collecting Dog Tags, as going through the main game itself is just 'meh'.
Now officially addicted to League of Legends.
Send help.