A few of my friends complain that the layout "sucks" or foobar lacks functionality they need, but for my use case, it's in a Goldilocks state. With that said, for people used to the functionality of Winamp, I think MusicBee is more likely to be the successor, in terms of out-of-the-box functionality and layout extensibility.
I see these complaints too, and I find them funny. The layout is what you make of it. I don't care for any of the layout presets presented in the "Quick Appearance Setup" dialog, but the default UI component is very easy to customize almost any way you want. There's even a scratchbox feature that lets you experiment with building a whole UI from scratch without messing with your current layout.
As for the functionality they find it lacks, well, there's probably a component for that.
Frankly I find foobar2000 comes with a ton of functionality out of the box that other media players don't have, like the very robust features found in the "Tagging" and "File Operations" context menu entries.
Out of the box, you could certainly customize it to have a similar layout to winamp even if none of the dressing looks at all the same.
My layout[1] is certainly very different than Winamp, but still conforms a lot more to the basic shape of Winamp than the usual giant screen-filling squares that are iTunes, Windows Media Player or the Spotify desktop client.
