There's really only two things you need to know about this one-shot story. The main character is really, really poor, mostly due to her own machinations. And the character is really, really strong. That's it. Every single joke is based off of one of those two points. And I mean EVERY joke. As you might expect, it can get really tedious after a while.
Thing is, Takahashi likes to pound jokes into the ground. And then pound some more. Supergal is no exception to this. She has created many humor-based anime and manga series over the years, but in a sense it's all just one big series -- because it's the same style of humor and same set of jokes over and over again. You can watch, say, any ten episodes of Urusei Yatsura or Ranma 1/2, and you pretty much don't need to see anything else she's done, because it's all just variations on the same themes, just in different settings.
In fact, if you look at the style of humor in 1986's Supergal, you can see strong echoes of it repeated still three decades later in Rin-ne.
That's not to say that Supergal is awful; it does have its moments. But there's nothing new here, it's all just retreading the same humor all over again.
