The whole image editor/animation import workflow needs a massive makeover! I don't think it has been touched since I started using C2 (about a year and a half).
Having all on those floating windows, when you go into image edit mode is horrible and it needs to be unified into one window, ideally dockable. You should be able to update an animation from an external source much more easily than the current way. At the moment you can't even multi select frames to delete them...instead I usually create a new animation to replace, import into this, then delete the old one...drives me nuts every time!
For instance in After Effects, I can replace referenced frames at any time or replace the files that are referenced at the source, then refresh. If C2 really wants to step up to be more like a pro DCC app, then it needs to be able to externally reference assets, rather than "baking" it into the project structure...which , granted, does have its benefits (all being in one location and zipped into a capx). Choice is always a good thing!
Animations should be able to be scrubbed through in the image editor and have a decent transport bar. As primitive as MMF is, it is miles ahead in this respect.
Before anyone whinges that you don't need enhancements to the image editor, since they do it all in PS/Spriter etc, well so do I, but having more robust tools in here definitely would help with quick edits and prototyping. At the very least add a view grid option for pixel art, some more robust shape tools (circle, ellipse , square outline), transform manipulator for selection (scale, rotate) and some basic fx like blur/glow. Both GMS and MMF have better tools in this respect.
And please fix that colour picker in the image editor, it is still glitchy on every machine I have tried, even though I filed a bug report on this a while ago. The colour picker used for picking background colours is far superior...not sure why it is not reused?