I saw Who Killed Cock Robin at Sundance 05, and yes, many people disliked the film rather strongly. Those that left before the Q and A session missed out, however, as a great deal of light was brought to the experimental nature of the film.
The main thing to understand about Cock Robin is that it is not primarily character or story-driven. The central focus is placed on the setting - the desolate wasteland of Butte, Montana - and its pervasive atmosphere of decay and hopelessness. Much of the film is told through image and sound. Dialogue, especially in the first half of the movie is sparse. What dialogue does appear, is improvised around a few dozen pre-planned scenes. Shot documentary-style on various media (hd, mini-dv, 8mm) the experimental bent of the film is an ultra-realism, conveyed by seemingly-aimless characters, conversations, and camera-work, that build on each other to create the rhythms of what it *feels* like to live in the wasteland of Butte.
If experimental and unconventional storytelling is your bag - definitely check out this gritty atmospheric film. If not, you'll probably lose interest VERY quickly.
Certainly not for everyone, but I enjoyed it.