Setpieces are technically impressive but rarely engaging, with the exception of the train sequence.
I think the movie's failures are mostly down to two things:
1) Not clarifying or contextualising the supporting characters. We don't get to know Swan, C, M, or the villain (can't say his name without spoilers, and can't remember the name they used in marketing) and so nothing that involves them is made interesting or personal. As I said with the setpieces, a lot of the movie is impressive only on a technical level, but isn't actually enjoyable. I lost interest in any of their motivations and had no desire to understand them either. Equally, much of the acting felt phoned in (Seydoux and Waltz), and regardless, the only character I liked watching on screen was that of Dave Bautista - ironic given that the character has no dialogue.
2) Its need to tie a thread through the previous films. It brings up some forgettable characters from previous Craig films and tries to make the story about them, but when I'm struggling to remember who some of these characters even are, there's little chance of me caring about this overarching narrative. This also ties into the poor quality of the movie's villain. We don't even meet the villain until the end of the movie, at which point the film attempts to do plot twists and finales that simply don't work due to the absurd pacing.