XFCE is fine. I used to use it and there is a lot to like.

It lacks tiling, and I use some KDE apps very heavily (Kate, Dolphin) so KDE integrates a bit better.

I have thought of giving XFCE another go and I do not think there is anything critical I would miss if I had a tiling window manager (which would have some advantages over KDE's tiling, I think), but I have KDE configured in a way that works for me so not very motivated to do it.