I've been running into the problem that 8 bits per colour channel is just too little in 2019. You get banding so quickly after certain combinations of operations, I can just feel the bits getting lost in the noise. You can see it by the histogram getting gaps and spikes. Especially with colour curve corrections.
It's getting harder to get modern quality images out of GIMP.
Also some tools that are available in Photoshop, like the many ways to smart select, or to crisp up a selection.
I almost only use GIMP any more for cropping and scaling, anything else, even if the feature is available simply lacks in quality of result.
I used to think the curve bend effect was pretty neat, to do certain types of distortions. But it doesn't do subpixel/anti-aliasing. Then WHY is it still even in there? It's not really that useful and it uses an ancient processing technique that really leaves wanting a lot in image quality.
I haven't tried the other tools mentioned in this thread, but I'm going to give them a try, hopefully they are better.
There's some good stuff on the roadmap for 3.0 and 3.2 as well: https://wiki.gimp.org/wiki/Roadmap