I also think that the treatment for Qhorin Halfhand and Jon Snow was not done well - unless they are going to alter the story in season 3, the viewers are left with a very different impression of this scene. And for Jon Snow, it is even worse, because it seems like he killed Qhorin Halfhand out of anger instead of a terrible call to duty.

I can certainly see where the changes for Talisa instead of Jeyne were made - it would be difficult to bring in that element in the novel for the series. This new love interest and character allows for Robb to find love with a very interesting female character without having to deal with all the political dynamics involved in the novels.