I wish for a menu editor to be included in Xfce. Other than that, i am quit happy using it. My Xfce setup starts at about 115 Mb's and it is very responsive in general. I do not use gnome system monitor or task manager -htop is just fine. Thunar with custom actions is my favourite and i find Xfce 's customization tools, easy to use and well organized. It outscores gnome here.
Some people prefer (just) openbox, other people fluxbox: a few -if any- gui tools, no impressive desktop effects, not a dedicated panel (for openbox) or a file manager! KDE is probably the full-blown desktop, plenty of bells and whistles, tons of customization options offered to the user -everything is there. You cannot compare it with Openbox, they are just different. It's all about preference -up to a point of course.
Mint's Debian+xfce really does feel "unpolished".
For my opinion, the reason for this is that it mimics gnome, Xfce-ness of the whole desktop is a bit hidden.