Manga Review!
I've only seen a little bit of the Manga and I'm really trying to get more of it.  This is what I know.
    The plot is about the same.  The Shinigami are detectives that investigate unatuaral deathes.  The bad guy is Muraki and sexually herrasses Tsuzuki and even Hisoka at times.
    Tsuzuki is still extremely sencitive about things and cries much more than in the anime.  He rellies on his friends a lot for support especially Hisoka.  In the Manga you find out that Tsuzuki has over ten shikigami (summoning beasts) while his fellow shinigami have only 3, at most.   You find out that Tsuzuki isn't fully human and Muraki said (to an extent)that Tsuzuki was part monster.  That really caused some mental and emotional trama to the poor guy and Hisoka had to talk some sense into him.  "You are a human!  Don't let what that bastard tell you get to you!" That's what Hisoka said to Tsuzuki in order to calm his partner down.
    Hisoka has it a little more tragic in the manga.  A lot of stuff happens to him and Tsuzuki is bailing him out as much as he bails his partner out of trouble.  In the Manga they talk about Hisoka's family a lot more than in the anime.  Also Hisoka is a lot funnier in the manga than in the anime and has a tendincy to be emotional when Tsuzuki's the only one around.
    Watari is just as weird as he is in the anime.  BUT! In the manga you get to see Watari working on a gender changing medicine to make himself into a girl.  He never manages to get it far as I know.  Experimenting on his friends (mostly Tsuzuki) is one of his favorite things to do beside blowing things up with failed attempts of his gender changing medicine.  In the Manga he usually stays in his lab with 003, a penguin, and a puffin.  Also he's partners with Tatsumi.  Don't quote me on that one, I really don't know what's going on between those two.