Project Overkill is a shoot ’em up game developed and published by Konami in 1996 for the original Playstation. The gameplay takes on a 3d-esque isometric view, in which the player chooses one of four mercenaries to lead through the levels. [Infos from Wikipedia]
My friend optiK sent me a link to this video (from Asuka120 youtube channel) and I thought it was neat: it is in fact from a pre-alpha build and most of what we can see in this early footage was not in the final game.
Video (Alpha version):
Video from the final game: