It was described as a 'sprint action shooter' and was set on a prison planet, filled with crazy convicts in plastic-model like world. It's okay you can forget it now.
It just wasn't up to snuff according to Square how scrapped the game, a decision likely influenced by Epic Games' Bulletstorm - the premier over-the-top shooter. See the Gun Loco trailer below for probably why the shooter was tossed.
Square Enix disarm Gun Loco
18 March 2011 | By Simon Priest