I have an uncomfortable feeling of swimming against the tide, but here goes...

I entirely agree that "half-baked" is just the sort of thing this critic might have said. It fits perfectly into the context. But does "de un solo hervor" actually mean that?

As a metaphor, "half-baked" (much more commonly used than "half-cooked") means "not fully thought through", "incoherent", "unconvincing". The idea of not being fully cooked implies not being fully executed or realised.

However, in cooking terms, "de un solo hervor" doesn't imply incompletely cooked or unfinished at all; it means that one "boiling" was enough to cook it. Not everything needs more than one "hervor". So I think the metaphor is a different one.

I think the writer is referring here to the metaphorical expression "no se cuece de un solo hervor" or "en un solo hervor":

"¡vos no te cocinas en un solo hervor! [...]
[...] se le atribuye a una persona mayor, dícese de la persona que ya no cae tan fácil en las argucias del amor, o que ya no te la cree a la primera.
En efecto, se refiere al cocimiento de una pollo tierno, es rápido y el de una gallina vieja, tarda bastante, cuando te lo dicen te quieren decir que ya tienes muchos años."
http://ar.answers.yahoo.com/question/index?qid=2010050419043...

"Lo único que habría que considerar es que son chicas grandes ya, no como las del año pasado que eran jovencitas, estas ya no se cocinan en un solo hervor..."
http://comunidad.tudiscovery.com/eve/forums/a/tpc/f/50710486...

"Algún gallo veterano, de esos que ya no se cuecen en un solo hervor, baila con las que le gustan menos para precalentar, para hacerse desear por la elegida..."
http://www.rincondeltango.com/chamuyo/textos/AfuegoLento.htm

In short, "no cocerse en un solo hervor" means to be old or mature (like an old bird needing to be boiled more than once). By extension, it strongly implies being canny, not easily deceived. Conversely, "de un solo hervor" means young, fresh, callow, and therefore naive and unsophisticated.

I like your own solution best.

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Note added at 4 hrs (2011-02-28 20:01:42 GMT)
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IMO, this is closer to the author's meaning. For me, 'half-baked' means 'not ready for prime time', whereas 'flash in the pan' would be something inconsequential that isn't going to be around very long. The meanings are very different. You might be able to choose better between the two meanings from other context that you haven't posted.