I fully think it was a throw away death but I don't know if I think it was quite fridge level. But, you know, I don't know if I'm thinking that because of my detachment from movie!Irene or what. To me, it did made some sense from a Moriarty point of view - just that how they did it was kind of lame and didn't make anywhere near the impact that it could have.

Holmes, Watson and Mary are the best characters - they could have honestly done without Irene in the first two movies and brought her in through the third and it might have gone better.