OK I'm having trouble counting to 3 but these are mainly in the same category, so I think it's allowed
Colour stuff:
-HSV colour picker (as opposed to HSL, Lightness and Value are very different creatures)
-Square colour pickers instead of triangular (triangles decrease in resolution in the corners, making it harder to pick the right colour, and it's fidgety thinking about which angle does what)
-Always-on resizable big colour picker in the dock (I can now only have a small triangle, and sometimes I want a BIG square)
-Customisablity of the big square colour picker (so I can control what is on what axis). For example, my favourite colour picker is from Krita, you can make it show Hue and Value in a big square, with a slider up top controlling saturation.
Look at this beatifull colour picker, hue on the x, value on the y, saturation in a stroke on top:
Note also the three small sliders along the bottom for adjusting/tuning in 1 axis.
Tool stuff:
"Hotkey" mode for tools. This is a killer feature from Clip Studio Paint, so simple and small but really improves the experience and possibility of reaching "flow state".
In CSP, if you hold down the shortcut for a tool, it becomes "hot", only active as long as you hold down the key. Then when you release the shortcut, it flips back to your original tool. It's delicious.
So youre making nice strokes with the brush, want to use the colour picker, you hold down 1 key on keyboard, pick the colour, then release the key to switch back to the brush.
All it does is save one click but man does it change everything, being able to so quickly switch between 2 tools just by holding your finger over 1 key instead of 2.