* Visuals aside, the UI is basically iTunes. It has the exact same elements in the exact same places, except Winamp looks like a tacky GTK+ theme.
* I couldn't figure out how to hide "Genre", which I strongly dislike, and "Year", which I don't care about.
* No fullscreen on Lion - this takes, literally, 5 minutes to add. I guess they would have to spend some time drawing a completely custom button.
* The largest UI element is the number of seconds that have elapsed in the current song. Is this really something that people care about?
* Sorting by artist seems to be broken - if I sort by artist, it should logically order each artist's albums alphabetically as well. I'm not sure what secondary ordering its actually using - it's not alphabetical by track or ordered by track number (all 1, all 2, ...). iTunes calls the manner of sorting that I suggest "album by artist".
* Scrolling is broken (not smooth). This is also an issue in Spotify.
* For some reason there is a prominent button to show the "About" dialog.
Good things:
* When the track changes, this list doesn't snap back to the new song. This is one of the most annoying features in iTunes.
* When the track changes, if you have searched for something, it doesn't just stop like iTunes. In iTunes, if you start playing a Beatles song, then search for "The Clash", if that Beatles song ends, it will not go to the next Beatles song, because the original song is no longer visible.
* Watch folders, which, if it wasn't ugly, would be reason enough to use it.