It's not so bad that Snape's character development, in particular, took a backseat in the OotP because the next movie title is in essence Harry Potter and Severus Snape. Alan Rickman will get a heck of a lot more screen time in the next movie, no doubt about it.

(What would it sound like if a Canadian said "No doubt about it"...no doot aboot it??? Hahahahaha!)