Poorly directed
Poor directional quality shines throughout this movie.
Dialouge is cut off too quickly
You don't really get to know the supporting cast. They just appear shortly from time to time and are just there to fill some dialogue.
There is no build up showing events prior to Alison moving into the apartment
Vital characters have too little screen time, such as the odd people in the apartment complex
Piss poor acting performance from Chris Sarandon, no depth, no emotions
Alison spends too little actual time in the apartment, and has little interaction with the other people there, which kills building up suspense
Michael's investigtion into Alison's experience at the apartment is too simple, is resolved too quickly and he just accepts that there's a paranormal component to his finds with no critical reasoning. When he reaches the apartment for his final showdown, he just accepts that there's an odd looking character at the top staring at him through the window, even though he's never seen him before.
Alison's father's death scene in flashback at the hospital is poorly done, with Alison's mother not given any significance. She just appears and disappears with no apparent explanation, and it happens very quickly. A couple of scenes and it's done.