Alrighty!
There doesn't seem to be an invert selection tool in the SCREEN$ paintbox, which is annoying if I'm working with text. After a while, the caption at the top of the paintbox doesn't change when I save under different names or load different files. (The caption at the bottom changes though.)
The names of the tools in the Tools menu don't exactly match up with the titles of the windows they create, and the windows they create don't make taskbar buttons, so it's hard to keep track of them. (I'm not a GIMP fan.

I'd prefer it if all the IDE stuff lived in its own window.)
Each window seems to have its own button for acting on its own data: there's a 'send to tape' button in the screen painter, and a 'add screen from blah' button in the tape editor. It's not a bad thing, but it's confusing for me as I'm unfamiliar with it. (It took me a while to realise that the 'add current screen to tape' option in the tape editor refered to the main output screen rather than the screen in the painter. (Though you can send the screen from the painter to the main screen))
I'll upload my game soon!