Being a student of cinema myself, I feel there are a few departments that always seem to fall short on many student films. Putting the obvious things like camera work, acting, and lighting aside, there are a few things that student films fail to do for me.
The first thing that will kill the mood of any film, in my opinion, is a lack of good production design. Because most students have no money, they end up shooting at boring locations which definitely doesn't help the audience's suspension of disbelief.
Another reason I find that many student films don't own up is because of their lack of a good sound. I know I'm not saying anything new, but sound is half of the reason we are captivated by the movies. It's just not focused on enough at film schools (well mine at least).
I'm sure there are many more variables that come into play, but I feel that those are some big reasons that many unexperienced student filmmakers don't achieve what they want.
Happy filmmaking,
Dylan