IMO, it's solid; not as good as Strahd, but that's not an insult!
I've only used as very small part of it -- my large party of ninth level characters stormed the Hill Giant hall, delayed until nighttime, didn't quite take out the watchtower before the alarm was rung, and then made an assault on the steading through the nearest door. It did not go well for them; giants normally not at fighting strength were rested and forewarned, and two characters died. I loved it.
I think that it's a great set of set-piece adventures. Each of the standalone giant adventures has an interesting hook: the giants have or want something, their environments are interesting to explore and varied, etc. I am less sure about the initial "atlas of adventure in the north" chapters, because I really am in it for the linked six giants adventures, and even those I'm not interested in using straight, but am instead weaving into my ongoing campaign. Looked at from my point of view, it's really great.
But if you're looking for something you can sit down and play cover to cover, I agree it might not be what you want. I find the motivations and setup in the storm giant chapter to be a bit weak; they hold up well enough for a one- or two- night adventure, but as the capstone to the whole campaign I'm less happy about it. I'm comfortable representing a room to the players without boxed text -- frankly, I prefer it -- which is good, 'cause there isn't any.
http://www.dmsguild.com/product/189...t-Upheaveal-5e?hot60=0&src=hnum&filters=45549 is free and the first chapter; as I say, for me that's the least
interesting part of the adventure (it just wasn't useful to me!), but it can at least give you an idea about layout, presentation style, etc.