I think the challenge is that there are so
many expectations. From reading and responding to issue reports, it seems like a group of people expect us to be Photoshop and another group expects us to be MS Paint - and making one group happy (non-destructive editing, for instance) annoys the other group. :)
GIMP is meets a lot of people's needs though (though we can always do that better). I'm in the process of transcribing interviews by GIMP's maintainer from professional artists who use GIMP and other free/libre software in their workflows, and it's really interesting to see what they're able to do.