Fallout has pretty good sci fi lore, but I was disappointed in Liberty Prime when I first saw in FO3. The concept seems very B-rate 50's sci fi. I know that Fallout has a 50/60's sci fi retro theme but that is in the art and not the writing.
One giant robot in terms of a military asset doesn't even make sense. Why not put whatever advanced weapon systems it has on a vertibird, tracks, or wheels? Those would provide better mobility and capacity than a slow, lumbering, easily knocked over biped. What's the point of it?