They say short films are harder to make, mainly due to the time constraints on telling a story, I'm not sure if this is true myself, the problems are different perhaps but both long and short are challenging in their own way.
Short form film is now achievable for most people with a smartphone and platforms like Instagram and Vine are great galleries for the imagination. However 15 seconds (or 6 in the case of Vine) is a tough thing to make engaging if you're an advertiser and your audience isn't just your mum and friends who are willing to sit through clips of your dog wading into the sea for sticks (guilty as charged...occasionally).
I came across Converse's Instavid for their Google+ Chuck Hack project recently, I can't seem to locate it on Instagram again sadly. It was a great example of short form advertising, creative, succinct and energetic. I then found out it came from a longer form film, a whole 45 seconds (see below), the film was made in collaboration with Studio Heiss and Jelly London. If you pop onto Flo Heiss' Vimeo page you can see some test films she did of the concept. I love seeing behind the scenes stuff like this as it reassures me that I'm not the only one who spends afternoons on their belly peering through a camera trying to test out some random idea.
You can find Flo Heiss' Wordpress blog, The Way Things Go, here