Figured it out- it's Descent (1995)

1990s Mac game.

First person in a space ship shooting at other spaceships in a large, maze-like area with metal walls.

There were little blue guys you had to rescue, but they were behind force fields that you needed to deactivate somehow.

I remember, vaguely, that the second level had enemy ships that looked a bit like crabs with pincers? I only saw them once so I don't know how accurate that is.

I double, nay, TRIPLE-check every post before I click submit, yet spaces tend to be randomly deleted somewhere in the postingprocess!

HELP ME PLEASE!!!