Fallout 3 would give more bang for your buck, but the game is riddled with bugs and glitches. The story isn't well executed, but the concept and atmosphere make up for that.
Metal Gear Solid 4, on the other hand, doesn't have more than a few hours of gameplay, but makes up for that with many hours of very well done cutscenes. You would most likely be buying a game like this for the story alone.
Depends, like the person before me said, MGS4 is more about the story than the gameplay, when it does come down to the gameplay, its more about stealth than action, so it would be a game you have to be patient with.
Fallout 3 has bugs and glitches, yes, but none that make the game unplayable/unbeatable as ive beaten it several times on my PS3, Fallout 3 is more action oriented and has quite a few rpg elements in it as well, very big open world, and pretty challenging at times.
Honestly, you would get more out of your money with going for fallout 3, but thats coming from a person who enjoys gameplay more than story in video games. Everyones opinion is different, but I just didnt like MGS4's gameplay at all, sold it within the first week of buying it(like 4 years ago) and never bought it or thought about it again. I didnt think MGS4 was as good as the earlier installments either.
How many amazon credits do you have anyway? Maybe I can help you get a game thats better than both of those combined and cheap too.
I see both your points and am trying to decide over story or replayabillity, but my only problem with fallout is that i own skyrim and i have put a large amount of hours into it like many others, but i found it to lose its magic after a while with some quests feeling like chores instead of epic adventures. I havn`t however found the glitches everyone seems to be complaining about.
I have $15 amazon credit by the way