(SPOILER WARNING)
It's good and nostalgic, but it gets a bit boring and some of the writing isn't my favorite. It feels like they're just trying to cram in as much information about the characters as possible, which is fine, but I think the writers could have done that in a better way. The first episode is info dump after info dump and I would have rather just figured that out for myself instead of every single character telling another character what they've done in the last ten years (They've all been together already, so I'd assume Spencer would know what happened with Freddie, etc). Nora shows up at some point and there's really no like reason/explanation other than she randomly ran into Carly one day and then starts following her around for no reason at all. Spencer gets mad at Carly and then makes a whole art show in an effort to offend her, which seems a lot out of his character. Then he randomly gets cancelled because of his honest commentary about the internet. The new iCarly web show itself isn't really shown except for one baby spencer scene in the beginning and one other with a "hater" from when she was thirteen.
Millicent and Harper are cool characters and definitely add to the show. Harper is super chill and seems like an awesome friend for Carly + has a lot of funny moments. I also really enjoy the dynamic between Freddie and Millicent. though I'm surprised Millicent gets away with some things that Freddie never would have when he was young, considering that they both live with Freddie's mom. But yeah, there's my honest review, it's definitely still a great show to check out for old iCarly fans who want to see what the old characters are up to + meet some new ones.