I have little experience with most of the books mentioned here. The only real candidate mentioned I have read and remember is Battlefield Earth. I read it as a child, heavily into my newly discovered love of science fiction, and motivated mostly by the facts that (a) my brother and sister had both read it, and (b) it was over 1000 pages long! This is when most books I was reading were 300 pages long at most. It was just a badge of honor.
My brother and sister both slogged through within a week each, so I was challenged to keep up.
At the time, I didn’t think it dreadful, but I know better now. I did like one little gimmicky idea.
The Psychlos have transporter technology, but they want to protect it from any stupid alien races like us slacker humans. So they have a control panel that has one switch that is changed every time the panel is operated. If you try to set the controls exactly like last time, it won’t work. You have to know to reverse the one switch. Apes like us humans would presumably see the board configured and try to replicate it and not be able to, because even if you memorized the configuration of every switch, it wouldn’t work.
I thought that was a dastardly cool concept, or the root of a dastardly cool concept. But the rest of it was pretty bad. Even then, I had issues reading it.
Harry Potter is not dreck. It may be a bit simplistic in places, and the later ones may suffer from a lack of editing for length and content, but it’s not dreck.
While I did read Jonathan Livingston Seagull as a child, I recall absolutely nothing about it. I even glanced at the description in wikipedia. Nope. Nada.
I have Clan of the Cave Bear sitting on my shelf waiting to be read, along with a hundred other books I have gathered but not gotten to yet.
Eragon was not dreadful. It might have been a bit derivative, but the author was 15 when he wrote it.
But honestly, for badly written books that get a lot of acclaim, nobody has yet mentioned Moby Dick. A couple years ago I decided to read it. OMG, it’s horribly written. Melville goes off on wild tangents. He writes a whole friggin’ sermon and subjects us to it. He goes on a long exposition about whales. There’s no story there, just chapters about whales. I gave up. The good elements have been extracted and condensed into other forms.
None of these are the worst books I’ve read, but the worst that have some sort of popular acclaim.
I would note the first novel by Walter Koenig (of Star Trek fame) as pretty bad, though I did finish it.
There’s one David Gerrold book that was so bad I did quit reading it: Under the Eye of God. I picked this up when I was in a huge David Gerrold phase, and a pretty big fan. This cured me.