I'm not sure about the close-ups either, but I think back then they helped make the game stand out. Other adventure games didn't have those close-ups. I remember for me, it helped flesh out the characters, and remind me that they were more than the two dozen pixels or whatever you normally saw them as. I agree, they didn't really fit the art style, but I think they still added to the game.

Also yay, new Monkey Island games!