To stay positive: kudo's for the improved looks and plans for improvements.
Unfortunately in real life, the dropped functionality has rendered Whiteboard completely useless for the types of creative collaborative sessions that I have been facilitating 
and inhibiting my daily work (not to say rendering investments in templates useless):
- Lists, likes on items and sorting by likes. This is a crucial feature for brainstorms (the new reactions look fancy, but don't work for our use as they are visual elements only). Also being able to go back to who liked an item is extremely valuable.
- Double click to view the entire board and double click again to zoom in on a specific part. Lacking the ability to bring everyone on the board to a specific spot this is a lifesaver in big sessions.
- Mentioned elsewhere: locking/pinning images us crucial when working with inexperienced users to prevent carefully created workflows from being ruined by moving everything around.
- Also: in existing whiteboards on which I locked images I can no longer move images around, meaning I have to rebuild them if I need a small change.
- images have gone wonky between users using the old app and the new one (visible to one, but not the other).
Not breaking but very inconvenient is the reduction in the number of pencils available. For creative sessions I often make business drawings using various colors and shades.... this takes a lot more time now.
For me this means that I have to go look for an alternative (shadow computing) solution for ms whiteboard and potentially have to cancel planned meetings in the meanwhile (this is unfortunately costing real money).
Microsoft