How about "it looks like a mess" or "it looks like every shareware image editor since the days of Windows 95" or "it looks like you crammed as many controls as you could fit on screen using a cross-platform windowing toolkit"?
I can't say any of that, it's rude - but it's what I'm thinking.
Look at the right hand side - count the scrollbars, the dropdowns, the counters. What's that hideous layer control thing that's like a treeview/gridview with nested scrollbars sized to suggest it should be huge, crammed into a tiny little space? Grim.
Do note that all that UI is crammed into a 978×722 pixel window; I would imagine it works far better on a decently sized 1280x1024 or larger screen. I bet you'd be pretty hard-pressed to get Photoshop or such to work well in that small of a space too...
Yes, its 100px wider, but still, imho Photoshop makes a lot better use of precious screen space. Compare the buttons under layer palettes. GIMP has 32px icons, while Photoshop has over 10px smaller ones. Or the slider, in Photoshop under "Navigator" and in GIMP in the Layers palette. Actually just compare Layers palettes in each. GIMP uses lots of superfluous labels and huge font size compared to Photoshop In my screenshot Photoshop also has 2 more palettes on screen.
Photoshops UI is also quite flexible, allowing to move and resize palettes freely, dock and undock, and group palettes to tab-groups. And layouts can be saved and then selected with just few mouse clicks. This allows it to scale across monitor size and count relatively easily.
edit: Sorry for inflammatory Photoshop vs. GIMP post
Photoshop (at least CS3, anyway) won't even install on a computer with a resolution less than 1024x768. Found that out when I tried to put it on my eee.
Sadly this is perhaps a measure of how desperate us GIMP users are. I'm just happy that GIMP is all going to be in one window. Its amazing that they finally decided to leave the old standard interface.
But relief and anticipation aside I have to agree with you that as far as aesthetics and design it is rather mediocre.
At the very least it is a start. Now that the maintainers are allowing the single-window mode to be created the onward march of open-source progress will keep improving it. It may not approach the elegance that Apple's designers deliver but we can sure as hell beat Adobe.
Edit: Did all of my downvote arrows disappear? I don't want to downvote anyone in particular here but that seems odd.
How about "it looks REASONABLY GOOD" or "it looks ABOUT LIKE YOU MIGHT EXPECT"?