I'm with Cinisajoy. If the app makes it easy to read the text it's just fine.
I would call an app garbage if it doesn't work; if it doesn't do it's job. Not if it doesn't work the way the big bad Wolfe things it should work.
Sometimes I think Wolfe has 2 categories: absolutely perfect and totally garbage.
I read on my phone more than a little bit with Moon+. I haven't the slightest idea what it does or doesn't do with CSS, nor do I care. Reading apps, like reading devices, are about reading, not about following a certain style.
Before I began using Moon+ I tried maybe a dozen or 2 dozen other reading apps. Most were just fine but I kept looking till I found one that scrolled, which I had been used to from my Palm days. Most Palm reading apps scrolled.
The only less than fine app I tried was Aldiko and it might have been fine too but I wasn't able to figure out how to import books into it. I finally gave up. I tried it again not long ago for some reason and even it was just fine now.
I'm not sure there are really any garbage ereading apps, or at least not enough that I found one while trying apps at random.
Barry