I just noticed the other day that Paint.Net does not have 4:2:2 or 4:4:4 chroma subsampling for JPEG. I think this is a configurable option in .NET, and it would be a reasonable feature to request nowadays.
There seems to be a bug where the [ ] keys do not increase or decrease the brush size. Ctrl+ clicking the + and - buttons on the brush size does do this however. Also it seems that the new way of registering brush movements is really inconvenient for brushing all the way up to an exact point. If I want the brush to reach into a particular area I now need to overcompensate the motion a little, which is a little frustrating.