Yes. It does suck. It's possible to learn it, just as it's possible to learn to ride one of those funny bikes that has the handlebars connected to the front wheel via a pair of cogs, so that turning left makes you turn right. It's possible to learn it, and even become proficient, and possibly even to make an argument that it's better for some definition of the word. But it still sucks.
Yes. It sucks too. Its use of space is inefficient, and the underlying implementation of it is exposed too much (I have to resize layers, rather than this being taken care of by the implementation automatically). That it happens to be ugly isn't really much more important than its dreadful name. They managed to rename Ethereal (wtf is that??) to Wireshark (good name, makes sense, lets you make jokes about frickn' lasers...). Why can't they manage it with the GIMP?. Yes, I know why they re-named Ethereal, that's beside the point.
In summary, don't cheap out on the UI because you want to use some open source UI library. Understand end-user expectations (i.e., not just YOUR expectations) and fill them.
Good advice. Trouble is, that's really expensive.