4 definitely takes a little bit of an adjustment period, but so far I like it quite a lot. I've mostly just been working on a choose-your-own-adventure style game and did some tests with a randomly generating endless maze demo with it so far. But I'm really liking most of the changes over all. Took a few days to figure out a lot of the changes, but it wasn't so bad after that.
Anyhow, something else I found myself really missing from my usual workflow in Krita is an alpha lock feature. Where you can click on an icon that locks the alpha values of all pixels while it is on. So this way you can define what parts should be opaque and alpha then have them stay as is while painting into the opaque parts with big messy strokes/stamps that would otherwise screw up the alpha without it. Alternatively, having a way to paint an alpha mask that is separate from the color map would accomplish pretty much the same. It could even be baked out into the alpha channel of the color map as it is now, just so long as it can be edited separately in some way.