|Pretty damn unique element, I'd say!|
Yes, you can argue that features need a different sensibility - you write for a global audience - and you write for a shared audience experience. You're not writing for the guy who's home alone and leaves the story experience several times to grab a beer, take a leak, etc. Cinema, ideally, keeps you in your seat, period. If you take e.g. cop dramas - TV will still allow you to get away with a ton of procedural stuff - where as film has the character front and center.
I've read an interesting comment somewhere: "The biggest difference between movies and TV is that in movies the viewer wants the characters to change and in TV the viewer wants the characters to stay the same." It's an interesting thought, think about it. In film - we want the character arc, we need the character to learn something, to change, to reach a conclusion, a resolution. In TV we often want and need the character to stay the same, to keep struggling from episode to episode and season to season.
With so much between TV and cinema blurred - there remains, for me, one major element - one thing that gives a story the right, the honor, the privilege of the silver screen treatment - and that one thing is the unique element. The "unique element", what is it? When I think of a story, when I think about a character, when I watch a film - the thought invariably crosses my mind - where is the unique element? And, let's face it, more often than not we're disappointed by feature films because we're watching rehash central time and again.
What makes a film unique? What makes it "deserving"? It can be anything really. An entirely new world (e.g. Avatar), a freaky fresh way of storytelling (e.g. Memento), a truly special character (e.g. Pulp Fiction's Vinnie). The uniqueness can be something big, but it can also be something small - a different way of looking at the world or simply a fresh twist on an old tale.
When you watch it, you instantly know when you're in the presence of something special, something fresh, something unique. When you're writing, it should be just as obvious to you. If it isn't, think about it. If you still don't know, ask others. It'll help you direct your energies and focus on the right medium (and collaboration partners, of course).
Find that unique element and you'll be on a special track that just may get your script made.