I read the series for a while, but stopped after (I think it was) the eleventh book. I just couldn't take it anymore, for several reasons.
My primary reason was largely for the way it had degenerated into a reverse-harem. Per se I have no problem with that sort of thing, but I'd be much more interested, and likely still reading the books, if the genders of the characters were reversed (e.g. it was a standard harem; one man with several girls he's screwing). I don't know if that makes me a hypocrite or not, but that did play a factor in it for me.
Another thing I didn't like was the blatant munchkin Anita was becoming. The way she kept suddenly and rapidly acquiring power in the later books seemed badly done, and it kept going on, compromising the way she was (in terms of power) outclassed by virtually everyone else. She was cool because she was the Executioner despite just being a normal human with a bit of necromancy. Now every supernatural thing in her city is scared of her just because she's her, and Hamilton keeps having to yank out bigger problems. The irony is that that's not in-and-of itself a bad thing, but compared to how Hamilton wrote the earlier books, and how no one around Anita can keep up at all, it comes off badly.
I also began to personally hate Anita as a character. Her whining about her misery as she's acquiring more and more power and so many lovers whom she's having incredible sex with was something I had less and less sympathy for. It's obvious Hamilton realized this was going on, and so tried to crank up the horrors to compensate, but it just didn't work (for me, anyway). There's only so many times you can crank out something awful before it becomes blase. Another crime scene where someone raped little kids and then tore them to shreds? Yeah, just like the last three books. Yawn.
Another reason I grew to hate Anita was for how much of a fucking bitch she was in regards to how she approached relationships. She pretty damn well demanded that anyone who wanted to be in a relationship with her has to play by her rules on absolutely every single fucking little thing, or they could get the fuck out of her life. At the same time, she was willing to bend only very slightly for other people. It got to the point where other people would point out what a huge double-standard she had, and she'd pretty much just shrug. I'm sorry, but I can't empathize with a character if, as a person, they piss me off so much.
Occasionally, I'll see a new book in a library or a bookstore and think of picking it up, but just reading the back cover or the inside flap will be enough to remind me of why I stopped. I managed to slog my way through two (or maybe it was three) of her new series of books, the Merry Gentry stuff, but it's the exact same crap as the last few Anita Blake books. Merry dives right into "I'm a slut, and I get stronger every time I put out!"-ville in the very first novel.
I just couldn't stand it anymore.