I wasn't sure about Jane going into this movie, but they did a good job with her. I really like the touch that it was Thor's wish to protect her that convinced Mjolnir to grant her powers (actually was it Mjolnir....see below). It doesn't take away from Jane's worthiness, but it does neatly answer the question, "out of everyone in the world is Jane REALLY the most worthy to get the powers?) It also ties in to something that happens later in the movie that I'll cover in a moment. But ultimately they handled her cancer respectably, and I was a fan of her death at the end, I think it felt appropriate, and it was cool to see her in Valhalla (though as a nerdy scientist is Valhalla REALLY going to be her ideal heaven? It would be interesting to see in Thor 5 her breakout because Valhalla "sucks" for her).
Jane's plot was one of those things I did not particularly like in the movie, perhaps because it doesn't have the same oomph the similar plot from the comics does.
In the comics, Thor becomes "unworthy" for some reason or other, and drops Mjolnir on the moon. He then goes on various adventures as "The Odinson" to try to regain his worthiness. In the meantime, someone else manages to summon and pick up Mjolnir, turning into a female version of Thor, and to begin with there's a bit of mystery regarding who the new Thor is. Eventually we learn that of course it is Jane Foster, who is battling cancer. But one of the horrid things is that when she transforms to Thor, Mjolnir purges her of all poison and sickness... but since the cancer is part of her, it can't do anything about that. What it does purge is the chemo, meaning that every time she transforms she backslides.