I think all the problems with Thor and Jane are people's expectations. Branagh made it clear in his commentray of the first film that these two characters were NOT in love with one another. There is no great love between them. By film's end he said it could be something more and that it was something the two wanted to explore, hence their desire to see one another, but again no love or anything. But for some reason a lot of people jumped to the conclusion that they were in love or something and complained about how ridiculous that was since they only knew each other for 3 days. They basically used that as an excuse as to why they were a poor couple, not realizing that Branagh actually agrees with them somewhat.
The problems come when we get to TDW and it's clear that Taylor or the writers had NO idea where to go with the Jane character. Unlike the first film, she was written horribly. I thought it was awful that she was so affected by Thor that aparently(according to Darcy) she spent all her time moping about him, to the point where she didn't even shower and get out of bed! This was the film that was supposed to explore how the two felt about one another but it was just handled so poorly and Taylor has admitted as such. Here's an excerpt he gave about Thor and Jane for TDW.
Its funny. We agonized for a long time, said Taylor. We thought the movie was about whether they got together or not. I think it came down shockingly late in the process that it felt sort of implicit that they were going to be together. So I think that point the reveal of
this is also a spoiler
Taylor continued, Who you have on the throne
was such a jarring thing that you couldnt follow anything else. So just that process, the finishing of Jane and Thor, wound up being a feel-good moment, but not a big story moment. The feeling was that instead of explaining why they were together, we just left them be together and then the final, final shot was one of my favorites. It was very late in the game, too.
So they didn't want to explain why these two want to get together, going into the film they didn't even KNOW if they wanted the two together, they apparently thought the whole movie was about whether they were gonna get together when it's anything but, and the final insult is that the reveal that they actually get together(remember, this WAS what the whole movie was about

) was BURIED in the after credit's sequence! It wasn't even important enough to put in the main body of the film!! Just awful. Branagh would have never let that kinda travesty happen if he had directed the second film
I was a huge fan of Jane and Thor in the first film. The second one just couldn't be bothered to adequately the develop their relationship. Going forward into the 3rd film, I'd like them to make a sincere effort in fixing these two, but if they'er going to put in as much effort as they did with the 2nd( which is none) I'd rather they just not bother.