I haven't seen the last two episodes, but I'm confident in saying the biggest problem this year has been that they're leaning on 'goofy Holt' as a bit of a crutch. That works on occasion because Braugher sells it so well and the character is so well established that things like him uncontrollably giggling at the taste of marshmallow or bawling 'HOT DAMN' are made to seem just on the extreme edge of his behaviour, but they're close to the point where each visit to that well deconstructs the character a bit more. It's not character development, it's just taking an established facet of the characters personality and allowing it to undermine everything else.