(Note I'm not saying I don't love it. Just not as much as I wanted to. My standards are pretty high and I'm factoring that in.)
Basically, I'm not sure if the series itself isn't doing it for me, or if it's genre fatigue, or if I'm just irked by listening instead of reading. Even though I'm on Grave Peril now which means I've been at it for a fair number of hours, in my own view I'm still pretty new to audiobooks. My mind wanders a lot, especially on a bike ride, and I keep losing my place and having to go back. Even then, it's entirely possible that I've missed some really important stuff which would have completely changed my outlook. The narration is great (hi Spike!), but it takes some effort for me to separate the voice from the story; the characters all end up sounding the same, and since it's first person and Dresden already has a bit of a magical PI thing going on, the noir aspect is emphasized too much for my tastes and makes me wish for visuals to go with it.
And as far as the magical PI thing goes, that might also fall under genre fatigue. I like urban fantasy and I can't really remember the last time I read a book in the genre, but it's all the heck over TV, and part of me kind of prefers it that way. There's never all that much variation in the setting; the devices in play are cool because they look cool. I don't particularly love werewolves, vampires, demonic intervention, or the Masquerade for their own sake, so if I'm going to fall for a story that uses them, it's going to have to do something new and unexpected. Either that, or just be a really, really good story that happens to use the urban fantasy backdrop.
I don't want to make it sound like I've already encountered every idea that the series uses, but generally, the encounters with the supernatural tend to follow a set sequence: introduction of a familiar bit of mythology, exposition on how it differs or doesn't from common belief, and Harry employing his occult power to use it or deal with it as needed. The last thing to pique my interest was the invitation rule, because I love the invitation rule and I've never seen it apply in various degrees, and to characters other than vampires. But that's a pretty small thing when the worldbuilding is so integral. It doesn't help that the narration is prone to "I'm a wizard" and "See, magic is...", which would be exciting things to hear if one believed in wizards or cared about learning a new magic system.
But the point is that the urban fantasy elements and the worldbuilding might be someone else's favorite thing just like me and the invitation rule (or, you know, if a telepathic griffin showed up or something). So I'm chalking all of this up to genre fatigue, or a trope distinction I've been thinking about: What's the difference between a wizard and a superhero? I actually thought about asking that question in its own entry, because it's not rhetorical, I really am interested in your answer. So if you care to, stop and think about it and tell me your conclusion before you continue on to mine.
A superhero has a limited number of trademark abilities, which are more or less static. A wizard (or witch, sorcerer, mage, etc.) can cast a spell for any purpose. It turns out I like superheroes more than wizards, which feels odd because I was a voracious reader of fantasy novels long before I ever picked up a Marvel comic. But with superheroes there's more dependence on a team of varied talents, and fewer openings for a deus ex machina. Or I just like designing characters based on one weird thing they can do that nobody else can do. So maybe this isn't genre fatigue, but it might be a little bit of genre indifference.
Evidence toward me just not liking the books/author is harder to pin down and perhaps nonexistent. I like the characters well enough, but I'm not that attached to any of them, with the possible future exception of Michael Carpenter once I see a bit more of him. I appreciate the humor though it hasn't made me laugh out loud yet. The writing style may not be especially quotable, but it's solid.
I guess all I'm saying is I need more time. If I'm still ambivalent after five books, I'll ask for incentive to carry on but probably won't give up. If I start to get the feeling that the problem is with listening, I'll try cracking an actual book.