I second this, Tcl is a lovely language in general and quite lisp like. One of the nicest and most unexpected experiences was learning it last year. Tk is then trivial from Tcl, with nice native GUIs being 15 mins away.
Tcl does have a few disadvantages, for one the lack of distinction between string and list types makes certain programs hard to write. Also the absence of lexical environment for the apply command requires awkward workarounds. Many Tcl users dislike expr syntax.
Warts notwithstanding, Tcl has allowed me to be very productive. Over the years it's been steadily improved, and yet remains mostly compatible with code written even decades ago. That's a rare accomplishment in the programming universe.