I've never had a problem reading text on my blackberry, or even books on my iPad - but since I got a Kindle I do far, far prefer it to the iPad.
Maybe that's largely a personal opinion or maybe most people would agree with me, but either way my point is - yeah, it's not "too bad", and is perfectly fine, but it doesn't mean it's not significantly worse.
YMMV, but I found reading books on my transformer a lot more comfortable after I switched the kindle app over to white-on-black rather than black-on-white. It was enough that I almost gave up on my actual kindle for a while.
All this pre-retina? I find pre-retina text display blurry to the point of distraction after long periods of reading. Also, how do you hold your iPad? I like the newest and cheapest Kindle's size and weight for holding it an almost any position for long periods of time.
The last 2 books I've read (the hunger games ones) were all bought and read on my 2 android devices (Galaxy Nexus and SIMless HTC Nexus). Cross-sync is awesome. I read on planes and before sleeping (you can invert the colors to have black background) The worst part is that I have an actual Kindle (albeit old)... somewhere. I don't miss it. At all. I love reading the kindle app on the phone anywhere, even buying the next one on the spot.
I have 2 Kindles, an iPhone and an iPad (latest generation) and I use the kindle app on them all. There's no issue with the iPhone and iPad - indeed there are times when I prefer them. The Kindle is also much better (at times) than using the iPad
I've read for hours on end on everything from a Palm IIIxe(Back-lit 160x160 grey-scale) and Palm T|X(320x480 color LCD) to a Kobo(e-Ink) and an iPad2. I've had no problems with any of them.