There are many reasons why mspaint is pretty ♥♥♥♥ compared to graphics gale:

To change colours you have to go to that edit colours window instead of just having colour options on screen all the time.
These apply to the windows 7 version:
All the brushes and shapes are now anti-aliased.
Where the click point of the cursor is is very slightly ambiguous/misaligned with the tools.

Now in Graphics Gale you have:
Up to 4000% zoom as opposed to 800%.
RGB and HSL sliders without having to go to another screen.
Displayed full palettes. (I have mine set to default to the CC palette)
Grid options for tiled work/sprite sheets, including snap to grid.
Layers (though I never use them).
Right click colour select.
Preview window that displays your image in 1x or 2x,3x,4x.

Actually MS paint has a super secret 1000% zoom only super leet MS Painters know of The rest I'll agree are handy, but I only like Gale for its color counter.