I think it's worth pointing out that in the years since this article was written (2006) quite a few new features have been added to Tcl. A few of the more significant include coroutines, robust object-oriented system, tailcalls, apply (lambdas), namespace ensembles, et.al.

Of course some of these features were already present in other languages. However, steady improvements to Tcl have pushed the language well beyond how it was described in the article. Definitely not a "toy" but overall as capable as the other scripting tools out there.