Since there is no confirmation on what the achievements will be for the game, aside from the time being, let's create our own!
Here's some of mine:
"KEEP IT CLEAN - 10 GS: destroy all environmental objects within the city."
"Terminator - 50 GS: Never use a health pack"
"Ray Charles? - 50 GS: Never use the low-light mode, VISR"
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"Keep ya pimp hand strong" - 0 GS: Get mauled by a Brute Cheiftain's hammer. "Over Nine-thousand!" - 15 GS: Score over 9000 points in Firefight on Legendary difficulty. "If only I were a spartan..." - 25 GS: Take down a group of 20 or more enemies on heroic difficulty or over (Campaign mode).