How is MGS not scripted? You have to go through the same cutscenes and boss fights as everyone else.
I'm not talking about the story experience, I'm talking purely gameplay.
You are right that in MGS you are required to stealth less than SC. MGS doesn't punish you from blowing stuff up and killing guys (well besides getting a lower ranking at the end of the game). MGS hardly punishes you for anything. Instead the game gives you the option to play however you like. If you want you can stealth through the whole game with no alerts. You can avoid even coming into contact with the majority of the enemies the entire game. Otoh, if you do get detected you can play it like a shooter and kill everyone. For people who like stealth and don't want to be seen or fight, MGS is very satisfying. Plus there's so much crazy stuff you can do in MGS like blowing up food supply buildings with C4 which causes all the guards to get really hungry and be more easily distracted by food sources. Or capturing snakes and throwing them at guards to scare them away. Or creating decoy diversions. Or camouflaging oneself and crawling through the grass unnoticed. etc...
Precisely. MGS is an open end linear game. That is, you follow a basic, linear path through the game but are given plenty of freedom within each isolated segment. This is actually my favorite type of experience, to be honest.
Crysis is like MGS on a much larger scale, basically. The game itself is definitely a linear experience, but each level is open ended and allows you to tackle every situation differently. That's one of the reasons I loved it so much.
Splinter Cell, however, offers no such freedom and forces you down a tube. On the flipside, some games go too far and open up TOO MUCH of the game (Assassins Creed is a good example of this). As Groove noted above, I'd love to see a mix of the two.
Well, if we're picking favorite stealth series then Thief is my personal favorite.
Yep. Thief II is still my favorite stealth game. It has been eclipsed on a technical level, but it delivered such an incredible experience over 10 years ago and other games just can't seem to match it. You had a perfect balance between linearity and open ended gameplay. Most stealth games go too far in one direction rather than finding the perfect median.