I love the tonal shifts, personally. With the set-up, it had the potential to be darker-and-edgier, and I think that really doesn't suit the 60s-Superscience-Nazis-with-Lasers aesthetics.
The guns are awesome, the fully upgraded shotgun is just mental (fires three rounds at once, the pellets ricochet around and it has a forty shell magazine.)
The bit with
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Hitler
is ace.