MGS4: Guns of the Patriots was an amazing experience the first couple times I played it, but when it comes to replaying it, I can't stand the game. Drebin is totally unnecessary, the bosses suck because they have no character whatsoever and are annoying with their poorly acted screams, crying, and laughing, the ending SUCKS, and there's very little room for interpretation. I rated it a 10/10 after I played it twice, but now I feel like it's a solid 8/10. It also infuriated me that you could have about 9 or 10 items equipped for easy access, but only 5 weapons. WTF?
I think MGS4 could've been polished out so much more. I don't even know where to begin.
Kojima would've been able to put out a complete version of the game if Sony would've allowed him to release it on two Blu Ray discs like it should've been.
I don't think he did fill up 50 GB.
But one thing he could've polished out is the stealth gameplay as you said. I need an incentive to use the tools he's given, because you can breeze through the game without using them. The game engine could've been better too.
There is so much that could've been fixed. But I really can't be bothered to write them down. The same goes for MGO. It's flawed in so many ways, especially the body mechanics. The idea and execution of the online play and features is brilliant. But technical blunders really tainted the game.
He couldn't because Sony told him not to. If he did he would've made the Blu Ray Disc seem pointless for ambitious devs leaving multiple discs to still be an option. Sony didn't want this, so they told him not to add and cut him off at one Blu Ray disc.