Got to disagree with you on this one yatzhee, they did majorly improve deadspace in this one. There was alot of psychological horror, that was put inbetween all the gore, that I really enjoyed. Yes, the necromorphs were actually the least frightening part again, but atleast we got to see Isaac with a personality, and grow more demented as the story progresses and the moments of mental breakdown grow more and more intense. It would have been great if they could have somehow combined these moments with the necromorps, because they turned into safe havens due to necromorphs refusing to interrupt Nicole and Isaac's "private time." Plus there are quite a few subtle things, they just get drowned in the bloodflow from the contant mindless assult you have to fend off.
But as for deadspace being serious, I would say: Yes, but it does have a degree of self awareness. Just look at the ending of DS2: A direct parody of deadspace1's ending.
Also, the helmet being so easily removable is part of the plot, so as ridiculous as it is, its atleast somewhat justified. Plus, people in the future will be lazy as all hell, which explains why the only person you control seems to survive more than 5 minutes in any deadspace game.