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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No F***ing Way - 500GS - Complete Halo 3: ODST on every difficutly only using a pistol. Weeeeeee! - 5GS - Get launched over 200 yards by a Wraith blast. Bulls*** - 50GS - In a multiplayer match in Halo 3 using any of the Halo 3 maps on the ODST bonus disk, get a Sniper medal by shooting somebody in the groin. m0nK3Y - 30GS - Get over 5 snipes from a second-story or high platform in FireFight co-op.