The boss fights are definitely a CMOA for Isaac Clarke. Clarke, an engineer manages to defeat creatures that slaughter pretty much anything else in their way.
When you finally kill the hunter it makes you feel prettygoshdarn good.
New Game Plus modus can be one for Isaac right at the start of the game. Image Isaac, arriving to a routine job with a Level 5 Suit designed for work in very hostile environments and highly upgraded mining tools, giving him an aura of being Crazy-Prepared.
Likewise being able to just take out the first Necromorphs that attack you instead of running away.
While it is a bit of a bummer that Isaac doesn't play a role in killing Mercer or Kendra, who all lead you to your position of utter screwedness, watching Kendra be completely liquified by the Hive Mind in the last chapter can definitely be considered a CMOA.
Though if one is quick enough, one can kill the Infector that's attacking Mercer's corpse before it can complete the transformation. And if you cut the bastard's limbs and head off, he'll be useless even if another Infector comes along. Perfect karmic retribution for this madman.
Dead Space: mobile
Vandal taking down the final boss in the Interquel for the iPhone.
Vandal: (Mortally wounds the final boss) "Great... C'mon, you bastard. I can do this ALL DAY."