Probably the fact that you can collaboratively work on the same documents as other users. Or that syncing files to local devices is pretty easy and straightforward. Sharing is also dead easy. From an IT perspective, file retention and versioning is a game changer. I just restored a computer that an angry user attempted to delete all files from when they had been fired because all the data was backed up to OneDrive. I think people just hate OneDrive because it’s often advertised. I think very few people who actually make full use of it, actually hate it.