I agree, there are a some missing filters compared to the likes of photoshop, including all the mosaic-like filters and hand-painted-like filters (don't remember the names but they are found in the filter gallery in photoshop). I also feel like the depth of field blur, radial blur and zoom blur should be able to be reversed. It would also be cool to implement smart filters but I'm not sure if that could be easily achieved.
I think we need drag and drop and an easier way to duplicate/copy/rename brushes too.