I'm curious because I'm reading an underwhelming book right now, and that has got me thinking about sucky books. I'm somewhere in between reading and giving up on The Friday Society. I picked it up because it has three heroines and I hoped that it might be a good female-driven plot. Also it's steampunk, and I don't care if the rest of you are tired of steampunk because I'm not.* It's YA but I've read plenty of good YA and thought nothing of it.
But it sucks. The characters are so badly done and there friendship is plainly forced. There is a romance stuffed in that is vaguely sexual assault like. And worse! The dialog period is period inaccurate! The characters describe themselves as "Hot." I can't. I don't know if I can go on with this book.
However, his is nothing like the worst book that I've read. The worst was Clockwork Rocket by Greg Egan. It has all the elements that should make me love it. It's hard science fiction and I seriously love me some hard SF. It has graphs! It has a truly alien species, with truly alien biology. BUT it just doesn't work but it's just too many supposings. The premise rests on a universe with incredibly different physics than this one. Which is okay, but then he expects the reader to follow the graphs and equations for an incredibly different set of physics. And then to top it off you have shape-shifting aliens (with a weird birthing process, and an equally weird death) and you don't even get a good description of how they basically look.
Either give me insane made-up physics or insane aliens not both at once, and don't expect me to follow your graphs. Not both at the same time.
*I remember years ago learning the term and being so happy that I at last had a word for what I liked.