I love the Harry Potter films, so Alan Rickman isn't my sole reason for investing so much into it, but I agree that he's definitely a show-stealer. However, although his screentime is short, I don't agree that he's simply reduced to staring at Harry Potter. In HBP especially, his role starts to take quite the dramatic turn and, imo, Snape is at his best when he's clashing with Harry.
However, Snape won't feature much in Part I. In fact, this is most likely the only significant scene that he will be appearing in because the focus is away from Hogwarts this time around. Part II is when he receives the truly meaty scenes, particularly with The Prince's Tale.