I was a long time user of AIMP (over 8 years). Actually I started using MusicBee this year because AIMP3 is very limited on managing big libraries.
The new style of AIMP4 is a bit similar to MB, but not too much. It looks nice but it's also quite inefficient (so far). Also it seems that is based on separate mini-windows (that can be closed/resized) instead of panels.
More details here:
https://translate.google.com/translate?u=http://www.aimp.ru/blogs/?p=573&sl=auto&tl=en