Amarok and gtkpod were both having Trouble with the iTunes DB on my 4th-gen iPod, so I took a chance and tried Rockbox 3.5.
It’s really nice, and I should have switched years ago! ReplayGain and drag-and-drop support are both very welcome.
As expected, the free software firmware’s interface lacks polish compared to the stock Apple firmware. There are layers of menus to stumble through and many options to configure, but it’s a very configurable and versatile firmware for those of us willing to put up with it.