I went into this completely blind, having never read the book nor seen any of the previous iterations...and I was a bit disappointed.
The main issues for me were the sudden shift from the first movie. I know they were never explicit about Pennywise's origins, but I was a bit surprised that the strategy was suddenly to obtain "tokens" to sacrifice and then stand around an old pot chanting to defeat him. That really came out of nowhere.
Plus, given that each member's retrieval of their token was the MAIN bit of action, it all felt a bit...laboured. The first few were good, but then it became entirely predictable; even down to the way, they kept faking a jump scare, then following it up with a real one. Plus, I TOTALLY agree with
@jivafox that the CGI became a bit silly; some of the transformations (i.e. the old lady) looked like they belong in Lord Of The Rings or Harry Potter.
And I really, REALLY hated the opening scene. It made me feel sick. I understand that it was from the novel and of COURSE, stuff like that happens in real life. I had to read a bit more about it after the movie, and it seems at least in the novel, there was some consequence to it. Here, there was nothing; it felt utterly gratuitous. It seemed like it was trying to make a point, but rather than make it towards the perpetrators; I took it as a warning shot towards the victims. I found the whole tone of it to be WAY OFF and genuinely think they got it completely wrong.
The saving grace was the cast; both adult and child casts were PERFECT (particularly happy to see Jack Scully from Neighbours popping up in a lead role). My favourite bits of the movie were the more whimsical parts that had little or nothing to do with Pennywise. Agree also with
@Raining On Me about the weird tone with the comedy. Out of context, there would be nothing wrong with it. But in the grand scheme of things, it felt muddled. Thinking particularly about the door scene towards the end; that could have been lifted from any generic, family-friendly comedy movie.
That's possibly the biggest gulf from the first movie; the humour from the childhood scenes happens very easily and naturally; I guess that IS how kids banter. Most of the stuff in the adult scenes, on the other hand, was placed and pointed and much less organically occurring.
I'm sure somewhere between the two movies; there is ONE good movie. But the second movie, for me, is not the pay-off that the first truly deserved.