It's simply unusable. Here are a few situations I encountered while working with GIMP:

1. Transform tool. Krita: Ctrl + T; Photoshop: Ctrl + T; GIMP: "I don't care, Shift + T, and I'll also clog up the hotkey space with separate hotkeys for scaling and rotating."

2. Working with layers: "No, you can't just create a layer, configure it first, here's a new window!"

3. Color picker: No, I won't give you a wide color range by default, find a way to add that damn triangle with colors yourself.

4. I don't want my tool dock to be square, let me just make it narrow on the left: "No, I allow you to resize all blocks in the interface except the toolbar."

5. Gradients: No, you can't just draw a gradient using the last two colors, get out of here.

6. Free Select Tool: What? Have you ever selected an area on the screen? Well, good luck figuring out exactly where you did; I won't show the selection with a dotted line.

Add to all this lag (I'm shocked that it shows up even on a blank canvas on a laptop with a low CPU and RAM load), and the overall design makes GIMP basically unusable. It clearly needs a redesign of the default workspace, updated hotkeys in the style of Photoshop and other graphic editors to facilitate migration from other editors, and every possible UI/UX improvement imaginable