Defiance: Vital Ground (DVG) is a very well designed and solid generic science fiction miniature game for 28mm or 15mm miniatures. The mechanics of the game are based around troop morale and training quality, and are aimed for staging somewhat bigger battles (several dozens of models per player), although they work for small skirmishes as well. With solid mechanics split into basic and advanced rules, tournament rules, scenarios and even a (fairly hard scifi) universe of its own packed into a single hefty volume, DVG is quite able to function as a "full service" science fiction miniatures game that adhers to a sort of "realism" as to the outcome of the decisions made at game time. However, it is still first and foremost a generic miniature system (hence the subtitle Universal Skirmish System) that features a very extensive army creation tool. The development effort poured into this and the experiences learned from the previous edition (the now-OOP Starslayer also published by Majestic 12 Games) ensure DVG is top of the line when it comes to producing balanced, variable armies from scratch or converting them from various other game system into a single rule set.
My more extensive review on the game can be read at RPG.net: http://www.rpg.net/reviews/archive/11/11318.phtml