Jane Foster is a character in Marvel Comics. She started off as the love interest of Thor. Unfortunately, she eventually replaced Thor.
Why She Sucks Now
She replaces Thor when she lacks some virtues to replace him, and he is doing his job well.
It doesn't even make sense that she's taken Thor's name as it's his actual name. That's like Barbara Gordon being called Bruce Wayne Girl.
Every story she's in is about "muh sexism" and straw man arguments about how anyone who doesn't like her replacing Thor is "being sexist".
It takes a long time for us to even find out this female Thor is Jane Foster, giving us little reason to care about her.
Every moment she is Thor, we are constantly reminded that our Thor is "unworthy". Unfortunately, most readers feel the opposite way about this. She is extremely pretentious. That tremendous pride is why Odin had Thor turned into Donald Blake. This case means that Jane should be considered unworthy to wield Mjolnir.
She refuses Asgard's offer to treat her cancer outta pride. This is quite similar to what Walter White did. She also made the real Thor promise not to cure her cancer for some reason.
Her comics have been repeatedly cancelled and relaunched.
The storyline of Jane Foster becoming Thor was done better in a Marvel What If.
The idea of her having cancer and using the power of Thor to make it worse could have made for a decent story if it had been better executed. Let's see if Taika Waititi executes it better when he adapts the Mighty Thor storyline in the MCU.