Alright, that's extremely broad, but I'll nominate some:
-Alice in Wonderland really isn't that good. I get that the point of it is that its writing style defies conventions, that it's a dream with a stream of thought approach, that doesn't make it GOOD.
-A Song of Ice and Fire could easily exist in a world without Lord of the Rings. There's a clear path of inspiration that leads to it (War of the Roses, Atlantis, etc.) that doesn't require Tolkien as a stepping stone.
-Brave New World>1984 (though they're both excellent).
-Farenheit 451 isn't that good, actually.
-The Jeter Blade Runner novels are so lacklustre, this is one of the few times I really don't care that something like them was retconned ipso facto (by Blade Runner 2049 and all the media that came with it).
-The Last Battle (of The Chronicles of Narnia) is bad, and if you like it, your opinion is bad. Also, Voyage of the Dawn Treader and Prince Caspian are the two best works in the series, while Witch/Wardrobe is pretty average, actually. Also, Charn is one of the most conceptually interesting elements of the universe.
-Brandon Sanderson is...I hate to say it, but he's overrated. The first Mistborn trilogy is pretty neat, but everything else of his I've read is generally average. I respect the guy as to the sheer volume of stuff he's able to pump out, but it isn't that great.
-Matilda is Roald Dahl's best work (if you disagree, go home, you're drunk).
-Superhero comics are imposssiblely dense for newbies to get into, and I'd wager that's why manga is kicking their arse in a lot of areas.
-Dracula is...it's bad, okay? It really isn't that good. I can appreciate the cultural legacy it left, but the work in of itself is bad.
-The Expanded Dune novels aren't bad, actually. They're not as good as the originals, but of the ones I've read, they're average space opera at worst. And of what I've read, there isn't much that feels incongruent with Original Dune.
-The Enderverse novels are a bizzare case where by all rights, they shouldn't work (in terms of writing style and arguably plot points), yet somehow do. That said, I can appreciate the less esoteric novels as well, such as the Formic Wars series.
-The Expanse novels aren't that good, and have a case of diminishing returns. The best element of the Expanse was its worldbuilding and mechanics, but by their nature, that gets less impressive as time goes on. In terms of plot and character...well, sorry Avasarala, I love ya, but you can't carry this series by yourself (nor can Bobbie for that matter).
-The Gears of War novels under Traviss are a mixed bag. On one hand, the IP owes them a great debt for fleshing the setting out. On the other, her personal politics...whoo, boy.
-The Halo novels get too much credit in a conceptual sense. They're not the only tie-in novels out there that have helped flesh out a setting, games or otherwise.
-The Harry Potter novels are pretty neat, actually.
-The Librarians novels are better than the show they're based on. Period.
-The My Little Pony comics are legit, in the sense that they're able to be a bit darker, and devote more time to worldbuilding. Deal with it!
-The Perfect Dark novels are the best thing to come out of Perfect Dark Zero given how they're able to flesh out the setting.
-Peter Pan (the book) is actually pretty dark, when you consider the full implications of it all.
-Ready Player One is a book based on VR, where the best elements of the book are those that focus on what's happening in the real-world, while the stuff that happens in the Oasis is pandering nonsense (yes, Cline, you CAN list 70s and 80s pop culture stuff for pages on end, I GET IT)
-Saga of Seven Suns is what happens when you have an interesting setting let down by mediocre writing.
-The best Shannara book ever written is Elfstones, which means that Terry has spent decades never reaching the heights he did in the early 80s. Sorry.
-2001: A Space Oddyssey (the book) is better than the film (while it's the other way round for 2010).
-Starship Troopers (the book) does not promote fascism. It does, however, promote militarianism. I think it's a good book, even if I don't like it much, either as it's written, or its themes/ideas.
-The new Star Wars EU stuff (under Disney) isn't too bad, actually. Yeah, there's some stinkers, but don't pretend the old EU was 100% gold either.
-There's barely been a single Terminator novel or comic ever written that has ever...EVER...really "got" Terminator. The closest I've seen was Timothy Zahn's works.
-Terra Nullius...okay, it isn't good, okay? Maybe that's just my "white fragility" showing, but even leaving the questionable historical parallels aside, the worldbuilding is highly questionable, as is the writing style (I can't think of any other novel where epigraphs are multiple paragraphs long, often coming close to 2 pages, if not further).
-Emily Rodda seriously needs to write adult (or at least YA) stuff in her World of Deltora universe, because it's actually pretty creative stuff, just, y'know, targeted at kids (yes, I'm being selfish).
-The Wheel of Time isn't very good actually. Or if it is, it happens after book 3 (where I gave up).
-Japser Jones (the book) needs to be stuided in Oz more, because it's the Australian equivalent of To Kill a Mockingbird. Mockingbird's better, granted, but JJ's far more relevant to the country it's set in.
-The Hate You Give's movie adaptation is better than the book. Cuts out a lot of the 'fat.'
-The Hunger Games novels aren't that good. It's one of the few cases where I can say unequivocably that the films are better than the books they're based on.
-His Dark Materials has the subtlety of a brick. Yes, I get it, religion is bad, I agree religion is bad, you don't need to keep hitting me over the head with it. Also, Lyra's kind of a twit.