MGS4 comes to mind. MGS1 had incredible writing with the occasional cheesy line. The plot and script in the fourth game was absolute 100% pure unadulterated hog tit with more cheese than a Boursin factory and enough half-baked pseudo-philosophical mumbo jumbo to sink the Titanic. It was unbelievably bad.

"Call me mama...BIG MAMA"

The second half of this video is just cringeworthy. What the hell are they even talking about? In fact, I could have picked just about any cutscene really. What also doesn't help is the rubbish voice acting. "He got old lol" is no excuse for Snake going from talking like this in the first game to sounding like a submerged HAM radio in MGS4. Actually, that codec conversation there is a good example of the superiority of the writing in MGS1 compared to its successors, and there wasn't even any animation.

Seriously, bring this up with me down the pub sometime and I will bitch about it for hours.