I think they're just a gimmicky thing and as a whole I don't care for them. I found them rather shallow, they change at the drop of a hat, and then you have those big obnoxious words telling you how your sims are "feeling," the annoying musical mood stingers (I know you can disable them, but I still think they were more of an annoyance than anything) and then there are the wacky overdone animations to go with them that make all of the sims look like a bunch of hammy silent movie actors. Added to that is the fact that there aren't many negative emotions and that the silliest things make them emotional. (Emotional over your decor? Seriously?) It's one of the things that has actually turned me off of this iteration. I always thought emotions were handled fine in previous games. I know my sim is sad, I don't need big letters telling me "SAD" next to his/her picture.
Then again, I'm not a terribly emotional person in real life. So, to have the entire focus of this game be something that I don't really care much about even in daily life is a bit of a turn-off.