I love his vehement defense of the 2D format, and I'd blame his reuse of sprites and lame 3D level design more on Konami's money-grubbing nature than IGA himself.
Pretty much the exact same thing I was thinking. It sounded like IGA always had a pretty pitiful budget to work with. I'd love to see what he could've done with a decent one.
My main gripe was his storytelling. I know a lot of people don't worry about the storyline either way, but it's something I would really like to enjoy, given the series' deep history. I really did like some of the things he did plotwise (Demon Castle War backstory, Mathias' reason for seeking immortality, etc.), but other things I either didn't personally like or found to be too absurd (creation of the Vampire Killer, Whip's Memory, etc.). But really, all he'd need is some help or editing from someone more competent with making a plot. Besides that, the only other thing that bothered me was the level design of the 3d games (but then again, that could go back to having a shit budget, too).
I really liked the gameplay in his games, though. Each 2d game he produced was really fun to play, and each one had an identity of its own. Although sometimes I thought his execution could've been better, I liked the fact that he was always trying to come up with new gameplay features.