As an avid GIMPer for ~12 years now, I hate the UI. It's only fine because I've struggled through it for so long and now I know where and how things are.
But it's really poorly designed and outdated. I completely understand and sympathize with anyone trying to use GIMP for the first time.
The application is perfectly fine for my needs and I'm ok with the ui.
But if you want something else, you can change that.
So grab the source code, try to get it to compile and run, and start making changes.
You have the freedom to do so. Use it. It doesn't matter that you're not great. Just do. No need to wait for others.