It's poorly written on a lot of levels. For one thing, the vast majority of the characters talk the same way regardless of age, background, or even being from Earth ("oh, crap!") This is actually one of the most immediate fixes of the TV show, the dialogue doesn't suck out loud because there's a team of real writers around Kirkman now. There's also the fact that almost all of the characters have the same internal logic, the same (immature, stupid, edgy) worldview. There are moments when you can tell Kirkman is legitimately trying to wax philosophical and it's just juvenile. The repetition in the way character's speak is insane. Like, if you took that to a professional editor they'd tell you you need to edit out about 66% of your dialogue in a lot of places. It's really just objectively terrible in a lot of ways.I don't see how its poorly written. I grew up reading Superman, and as a supes analog its far, far better than anyone superman story arc I've ever read.
My problem with Invincible is people pitch it like it's some Alan Moore shit just because it's aware that it's a superhero book, but it's still very much a juvenile superhero book. If you enjoy it for what it is: big, dumb, loud, entertaining superheroes? Then it's pretty cool, and I am a fan. But it's nowhere in the vicinity of a well-written story, and should never be mentioned amongst the best superhero comics ever written.