I'm fairly competent at drawing pixel art, and I've always enjoyed using the editor because of its simplicity. That said, the editor is such a dinosaur. I was using long forgotten editors, some with better features, back in the Amiga days. And I made own graphic editors with some better features on Amstrad cpc 464. I don't enjoy knocking Clickteam, I love their software, but the graphic editor has barely changed since the Games Factory.
Just two extra features would do me:
Tile editor - so you can easily make seamless tiles.
Layering - so you can make some changes to graphics without destroying or having to make multiple copies of the original.
But why stop there?
Preset palettes - atmospheric palette selection for themed levels like forest, desert, snow.
Palette generator - so you can grab palettes from inspirational images.
I'm only asking very basic features here, but there's is just so much room for improvement.