Having used some Froyo/GB devices in the past and now full-time using JB, Android just isn't there in terms of visual quality. Let's take something simple. The font. It's just not... Right... It's thin. It's stretched tall. The drop shadow is almost indistinguishable from the lettering.
Icons are inconsistent and difficult to distinguish. I often tap the Google Voice icon when I meant to tap Google Talk. Yes, I know the icon says 'talk', but just glancing at the two quickly it's hard for me to differentiate between the two. I have the Google Maps and Google+ icons next to each other and they're even hard to tell apart from a quick glance.
Everything feels just not well thought out. Why, for instance, since Android devices tend bigger, are menu options and navigation in apps not at the bottom of the screen. I can't count how many times I've gone to open a new tab in chrome and instead of hitting the 'new tab' button, I hit the current tab and it just reopened and I have to do the whole thing over and just stretch a bit farther.
It feels like Android is a collection from a lot of different departments just kind of thrown together and released. The main OS functionality from one department, but the GMail app is by a completely different team. And then the Maps applications comes from somewhere else. And then the Navigation app comes from somewhere else. the Google Earth app is from a whole other department. Nothing feels cohesive.
iOS is in an entirely different league in this regard IMO. JB, and even ICS that I've used on a RAZR, is a LOT better in terms of UI, but I don't even think Google even showed up on the playing field in terms of usability for me. Now, your definition of usability and ease of use may not be the same as mine, and some things that bother me might not bother you. I get a lot of eye rolls from friends when I start talking about things like "fonts", but it's important to me. I stare at it for hours a day. I think sometimes people lose sight that what they do or what they like is the end all be all of what anything should be and that there's no room for anyone else to dislike what, for them, is perfect.