This editor deserves a higher rating and will get one if more work is put into it. It is already a very good tool for animating sprites, with some added tileset features. Curiously, I found the tile grid handy for working on tiled sprites. Piskel and Aseprite don't have that.

There are, however, little bugs and other annoyances scattered here and there that betray a lack of extended development based on feedback from diverse users... perhaps because it is unclear where or how to leave feedback. The most obvious thing missing is a line tool. In fact, trying to draw a line with the rectangle tool instead leads to no line and a bug where a narrow rectangle appears in the previews (if on a cell other than the first). Select-and-nudge operations could be easier with arrow keys enabled for nudging while a selection is active and/or a modifier for dragging while not leaving the select tool. I also ran into some strange behavior when trying to paste semi-transparent pixels from one cell onto another on top of solid pixels (the alpha pixels turn white). I have other things I could remark on but I can't remember them all at the moment and that is enough for now.