Beauty is in the eye of the beholder. I think Pidgin is quite nice to look at. Nice and standardised. Flashy graphics are nice, but they don't help me chat. I hear what you're saying about missing features, it's definitely frustrating, but you have to consider that most of these clients are designed for multiple message formats, and there's often discrepancies between them. The majority of the IM protocols owned by companies (think, Yahoo, Google, Microsoft) don't release their protocols either, so much of the work is done by reverse engineering, meaning that the unofficial clients can have a hard time working with these proprietary formats.
Did you try the YIM web messenger? Not ideal, but I'd imagine that it would be feature complete. Probably the closest you're going to get at the moment. You can try running the client through WINE too, although the Wine website doesn't look promising with regard to running the YIM desktop client (WINE isn't really related to Windows at all, other than the fact that it can read Windows binaries and implements some of the core Windows libraries required for applications to run. There's nothing to say you can't create an application that runs in Wine that doesn't run in Windows).
Yeah, web messengers are not a solution for me. There's ebuddy, that one I liked, but I hate that it works...well, in a browser window
I hear what you're saying about the need to reverse engineer those apps, but I wonder how hard can this be, compared to building alternatives for other Windows apps, like Photoshop/GIMP, Sound Forge/Audacity, etc. So if someone can reproduce all these things that Sound Forge, for example, does, like vst plugins, effects, etc., how hard is to create an app that does what a IM client does? I don't know much about how these clients work, so I'm literally asking. And it seems weird that on Windows we have quite a few nice IM clients that support multi-protocol...didn't they have to reverse engineer too, or something like that?