I didn't say I wanted the film exactly like the book, I said I was disappointed at the changes made in the second part. I quite liked the first film, and it changes many things from the book.
But the characters in the first film mostly feel the same as the book versions and the general tone of the film fits the book (if being a little less horror and more Goonies-style adventure, but there's a bit of that in the book as well). It could certainly be darker, but there's a limit to how gruesome you can get with a film, and they're at least willing to show kids lose limbs and bleed out on the street.
The second film just falls a bit flat in comparison, mostly because rather than making minor changes to characters and cutting some of the less important scenes to shave down the running time, it makes significant changes that leave some characters having little to do in the story and doesn't really further develop the world and even ignores some of the subtle nods from the first film. It just doesn't seem to have the same care put in it. Pennywise isn't lurking in the background of every scene like he is in the first, the town never feels like Pennywise is manipulating the residents (outside the opening scene which is straight from the book) and there's nothing as creepy as the projector scene or as gory as Georgie's death.
The second film just isn't nearly as unsettling. And I contend that a big part of that is the choice to leave out most of the lore that fleshed out Pennywise as an otherworldly horror. Instead of being an Eldritch abomination from beyond the stars, with the added metaphysical issues the book brings up by killing off the Turtle, this version of Pennywise is just a weird alien-thing who chooses to look like a clown for some reason. And then he gets killed by mild insults and curse words. He goes from being an unkillable, waking nightmare in the first film who is perpetually watching the kids from the shadows and controlling the adults to further isolate the kids from any possible help, to being a shape-changing alien who couldn't last ten minutes in an online chat.
But as you say, you've never read the book, so it's probably impossible to understand how underwhelming this version of Pennywise comes across as.