The 4K streams I have tested have all looked great.
Moana especially.
No lies detected about Moana. Looks great in Dolby Vision. The contrast between the dark scenes and the torches at 28:00 are an especially good showcase of the quality and tech.
Frozen is decent but not quite as good in the Dolby Vision / HDR department comparing a somewhat similar light contrast at 1:15:00 - so there's some inconsistency compared to the Apple TV+ gold standard quality across its titles.
However, comparing HDR consistency to Apple TV+ is not really fair in any way to Disney+ considering the sheer difference in volume and back catalog. Apple TV+ is a comparatively tiny assortment that must be way more realistic to enforce DV/HDR quality control.
The good news is that Disney+ shows us it's capable of living up to that standard with future new content.