Weird isn't it? First, everyone wanted it to look flat. Then Win3.11 had mild bevels. Then Win95 had more bevels and 3d look panels (sometimes recessed, which just involves drawing the two lines the other side of the panel...). And then things went really squidgy-looking with GNOME, and then it has gone flat again.
I am not sure what people want. At least buttons look like buttons (unlike the way iOS and other mobiles OSes are going). Is it a button? Is it a plane? No, it's text! You end up bashing your screen as it isn't obvious what to press. My mum is really confused.
You can change many aspects of the look of GTK+ with themes. You can probably even make it look nice and flat, in keeping with the latest UI fads.
Personally, I think XFCE looks nice out of the box (in Xubuntu, at least). And what's a better alternative? Unity and GNOME are both way too dumbed down for me, and KDE is both ugly (IMHO) and and quite buggy.
