Funnily enough I'd never used Tcl until I started tinkering with FPGAs, and while initially I hated it, I went through a process of developing a grudging respect for it, and now actually quite like it!
What I will say is it's absurdly easy to write a Tcl extension - I wanted to talk to a soft CPU using a Xilinx Platform Cable USB (which isn't supported by OpenOCD). I ended up creating a simple Tcl extension around xc3sprog and it worked a treat - I'm pretty sure the engineering effort to do the same for a different scripting language would have been much greater.
What I will say is it's absurdly easy to write a Tcl extension - I wanted to talk to a soft CPU using a Xilinx Platform Cable USB (which isn't supported by OpenOCD). I ended up creating a simple Tcl extension around xc3sprog and it worked a treat - I'm pretty sure the engineering effort to do the same for a different scripting language would have been much greater.