I want to be nothing but encouraging, but I have simultaneous positive and negative reactions. On one hand, we need better FOSS alternatives to imagemagick, on the other hand, using imagemagick as the target to compare against means it's doomed to repeat some of IMs mistakes. And sure enough, using the online server's filter examples, so many of them seem to exist to fill a checkbox and increase the filter count, but…
Could you please mention good filters, both free and commercial, that you think "aesthetically pleasant to boot"?
What makes filters more ugly to me is filters that aren't very functional as a building block or a node in the middle of an image processing graph. When I said aesthetically unpleasant, I was thinking about design too, not just the aesthetics. Filters that include any aesthetics at all, frankly, are not very useful, and that is the main problem with many of G'MICs (and ImageMagick's) filters. Photoshop has some too.
I'm using https://gmicol.greyc.fr/ as the reference for filter names.
G'MIC Filters that are useful as a building block (filters you're likely to find used by professionals), and are not aesthetically unpleasant:
Basics, Colors|Channel Processing, Contours|Difference of Gaussians, Degradations|Blur, Details|Sharpen, Repair|Upscale
A small sampling of G'MIC Filters that are aesthetically unpleasant to me, primarily because they are poor building blocks (less likely to be used in professional work), secondarily because they add an aesthetic that I personally don't like, and try to do too much:
Arrays|Puzzle, Artistic|Ellipsionism, Deformations|Rain drops, Frames|Tunnel, Lights & Shadows|Shadow Patch, Patterns|Hearts, Rendering|Cupid, Sequences|Lava Lamp
Note that many of these could be re-created easily using proper image processing building blocks, like an over operator for compositing, or an expression node for image warping.