This is all great stuff, though I'm not sure we're coming to a consensus
Most agree that the spell is too powerful as is, and people are obviously house ruling it (upping the levels of targets it can affect and giving a saving throw seems to be the most fair).
I like Ferret's concept of describing the spells' different effects by describing the spells as doing something slightly different (a telling off, rather than a lot of rude words, etc). But at the end of the day, (I MUST STOP USING THAT PHRASE!) the four spells are supposed to be equivalent. The whole point of spell design is that spells of the same level are of the same power; and these spells aren't just that they are the same concept (just for different alignments)!
What really winds me up is that this is a prime example of where Wizards have nerfed our game; with, let's face it, a tinkering with a system we were all just learning to like, for financial gain. Now I don't mind them making financial gain, if they didn't we wouldn't get any product, but it is the responsibility of the producer of a product to provide a well-thought out and tested product. Too often, problems arise in a 3.5 game that arise because of badly thought out concepts and not enough proper trialling.
Now I know that Wizards will claim that they were only responding to our responses to 3.0, but if that was the case, why didn't they ask us IF we wanted a revision?
Which brings me back to Blasphemy, and funnily enough, Sleep! Sleep has been severely ruined as a spell for any Bard, Sorceror or Wizard to want to take. The reasoning for this was because it was a spell that could give an instant kill, and Wizards thought that this was to be avoided. Yes, good point, but did anyone (has anyone ever) complained about Sleep (a core spell for always)? Then look at the effects, or consequences of Blasphemy, et al...
Potential instant kills? Yep. Nerfed? Nope. HUH!? Logic error...does not compute...bzzeiaarp!