We decided right to the start that we wouldn't do a horror or a thriller film because we thought it was too cliche and it seemed everyone else was doing it. We thought that sci fi might be a possibility, but then realized that it would take way too much effort and money to buy props, set up settings and make it look vaguely realistic. We decided a western could be a good idea so long as we didn't stick to the typical status quo of gun toting cowboys and bring it up to date. For instance instead of two groups of men facing up to have a duel in some outcast mexican town we could have two rival gangs facing off down a suburban park or public place.
Other ideas were to have an art house / surreal look to the film, eg David Lynch. Or to have a mockumentary, based around somebodies lives. A third idea was to have Phycological Film Noir.