I greatly enjoyed the game, but personally I thought the Homicide desk was the most disappointing.
Spoiler:By the time you've finished the first or second case of the desk, it becomes pretty clear that you're just being set up with red herrings, so everytime I went to a crime scene and found yet another Dalhia victim that would lead me to yet another false arrest, I got frustrated.
I really enjoyed the final Arson desk, especially the action with Kelso. I love Phelps as a character, but Kelso's willingness to go above the law when he needed to just felt more film noir to me. I also liked The Fallen Idol, The Black Caesar, Manifest Destiny and all the DLC they've recently released - especially The Naked City (Nicholson Electroplating started out great but ended way too abruptly for my tastes).