1000 Misspent Hours has this to say:
And of all the dubious films in the genre to bear the Universal imprint, perhaps none is so eminently worthy of its creators’ shame as The Deadly Mantis.and
The damn thing is only 78 minutes long, for God’s sake, but it seems to take at least three times that because so little of that time is spent moving the plot along. But it has a really cool, really crappy monster, and ultimately, that’s all that matters.
Moria calls it "predictable" and "fairly routine".