I watched Ga-Rei Zero despite numerous warnings from various people not to. They alleged the show is terrible, but I was willing to hazard that to find out what the deal is with Yomi. I won't tell you much about Yomi, but I will tell you people were wrong about the anime being terrible. I can understand why some people don't like it, though. First, Ga-Rei Zero pulls the rug out from under the viewer numerous times. [Spoiler: The lesbianism is a lie.] Moreover, the show does not take itself too seriously, and borders on self-parody on a few occasions. I can understand that some may also dislike the shifts in tone, but I rather enjoyed them. Finally, some complain the anime isn't true to the manga. Those complaints I don't really understand.
I've started reading the Ga-Rei manga. (The Ga-Rei Zero anime is a prequel taking place two years prior to the opening chapter of the Ga-Rei manga.) I've completed the first 25 chapters, and I have to say the anime does not stray far from the spirit of the manga. Yes, there are notable differences, particularly in that the manga is told from the perspective of a male lead. I almost dropped the manga early on because I thought he was another shounen jive male protagonist, to tell you the truth. But while there is a lot of "I'm just a normal guy...except I can see ghosts" and a little too much "I MUST PROTECT HER!" there isn't much Bleach or Index-type exposition. Mercifully, the manga also does not take itself too seriously, and there are a lot of tongue-in-cheek jabs (including a ridiculous first kiss). There are even some tanuki jokes I know at least one person will appreciate. There's also some well-drawn fan service to go along with the admittedly shounen jive overall plot. My only real complaint with the manga is that the comic timing seems a little off. I can see the framework for the jokes, but the effect loses a little something in the translation. I suspect Ga-Rei likely reads a bit funnier in the original Japanese, but that's just speculation on my part. Oh, it also needs more Yomi, alas.