I implemented a gui for SimCity in Tk, and at the time (~1993) it was the best user interface toolkit for X11 available, but only because the competition was Motif and its ilk. The reason it was relatively good in that context is that it had a built-in scripting language: TCL. (So did WINTERP, but that was XLisp + Motif, so Motif made it suck a hell of a lot more than XLisp made it win.)
As a scripting language, TCL is terribly designed (but beautifully implemented). But all that mattered at the time was that there was a scripting language that was present at the time the GUI tooklit, Tk, was designed (so they did not overlap and squabble about what they were trying to do) -- not that the scripting language itself was any good. (Personally, I'd MUCH rather be programming GUIs in PostScript than TCL, which is what I did before, for the previous port of SimCity to NeWS.)
The fact that TCL was an integral part of the design of Tk from day 1 made it possible to use the scripting language for what it was good for, instead of Tk trying to do that in a half-assed non-turing-complete way: to glue everything together and do all the dynamic symbolic stuff, binding events to handlers, creating objects, naming them, plugging them together. All with wonderfully flexible simplicity and generality. Instead of trying to wrap the X Toolkit Intrinsic's and Motif's lame overlapping and incoherent attempts at object oriented programming, configuration, skinning and event handling in C and .XDefaults files.
Here's a typical TCL file that creates an instance of a SimCity editor window (it's more complex than a typical less dynamic TCL gui, since it's capable of creating any number of independent editor window instances, which is why it uses a $win prefix for everything it creates):
https://github.com/SimHacker/micropolis/blob/master/micropol...
No matter how much you love Lisp, WINTERP was still just using it to wrap Motif, even though Motif was suffering from a terminal case of Greenspun's tenth rule, and contained its own ad hoc, informally-specified, bug-ridden, slow implementation of half of Common Lisp.
Here's WINTERP:
http://nielsmayer.com/winterp/