I use Tcl::Tk on a regular basis and really happy with this. After some 10+ years of usage of this approach - I understood that this is the perfect balance of simplicity and power for my GUIs.
Nicer GUI libs often require more efforts during coding, so I haven't switched to these.
often I use pure Tcl CPAN module instead of Tcl::Tk, because I rarely actually need that perl/Tk syntax,