Personally, while at my age I can't get excited about a hunk of noisy plastic, I can say this: the target audience loves these creatures, and who am I to argue with that? My daughter is 5, and treats her Zhu Zhu Pets as members of her extended family. They drive mom and dad nuts, squeaking and honking, but it's a small price to pay for her smiles. As to robustness, for a moving toy with electronic parts they're very well constructed. They're the kind of toy you can step on with a fair chance of not damaging it, drop from small heights from small hands, and they have only one drawback -- when the batteries run down, some of them will spontaneously chirp. And that's not a sound you want to hear when you've fallen asleep on the couch. ;-)
Seriously, these things are gold for kids who like them and well-priced and well-made, but it is a matter of taste.