Spoiler
Overall I enjoyed this series. I didn't really like the first part with Wataru's lack of presence, but it set up the story for the rest of the series. I think the "Faiz loses his belt every other episode" of this series was "Wataru's depressed again" though. It was a little grating for the plot to be set up so that Wataru was always being thrown back into a state of withdrawl.
There were a lot of little things, really, just minute things that took away from the series from being really awesome. The LOL, more time traveling bits (which I admit, were actually done pretty well). The useless one-time toy fodder (the big head bike, the super powerful awesome wonderful upgrade to IXA, Castle Doran, transforming Bat Kiva, the arms monsters). I don't think anyone enjoyed the "new Kengo" subplot, it just seemed completely unnecessary
Just to be nitpicky, it bothers me just the slightest bit that there's no distinguishable advantage from any of the IXA form upgrades. No explanation of what Kiva and Kivat are {I guess we can assume they're just Fangire technology, and IXA was based on them, explaining why IXA can use Fuestles?}). I mean, they didn't explain what Den-O or Zeronos were either. Since the series are all about these guys ant their powers, it seems like sloppy writing to just not explain where their powers come from or why they work the way they do. To the very end Megumi had Nago jumping through hoops while blind just so she could let him use IXA. I suppose that was supposed to suggest that she loves him, but c'mon, that's frustrating
I hate Kiva, I love Wataru like a pupil. I'm a dick, I'm Shima's dead. No, he's alive. Maya's dead. No, she's alive.
But post episode 24 I thought the series really kind of took off. I thought the Mio plot added a lot to Wataru's dimension, even if love always ends tragically in a Kamen Rider series (maybe the KR writers should see a psychiatrist about that). We saw less of the more charismatic 86 cast, but they were still pretty important. Both Otoya and Wataru really start to change once they meet their fated woman, and that visible growth is kind of nice.