I have mixed feeling about the hierarchical facility in statecharts. I've certainly found it helpful in some cases; for example, handling "cancel" events that apply to a group of states.

I've also seen huge, multi-level, multiple-parallel-region monsters that were impenetrable.

Now, no formalism is immune to abuse: "just because you can, doesn't mean you should". But I've often found that the simpler state model formalism - without hierarchy - has led to cleaner design and better separation of logic.

More generally though I do think state machines are somewhat underrated tools in the programmer's toolbox.