Nothing says easy XBOX 360 achievements like a game with cheats that won't disable them. Each game disc contains its own unique codes for unlocking the cheats, however, there is a method taken fromhttp://tinyurl.com/mq7baathat explains how to get 3 of them. It may be only 3, but they make this game an easy 1000 points in just one day.
Once you have unlocked the 3 cheat codes (Infinite ammo, Fast Health Regeneration, and Extra Damage) begin the game on hard. I know below that some of the level completion achievements say to complete it on easy or normal only, but completing them on hard will unlock them as well.
Below on another tab are the achievements just for reference purposes only. They are self-explanatory so I will not go too in-depth with them. I will instead give some tips on how to complete this game in one play through while unlocking all the achievements.
It may take somewhere between 10-15 hours to complete, but only because the get 50-250 headshot, melee kills achievements are a little time consuming. There is a spot in "The Low Road" level where you can sit and kill an infinite amount of respawning enemies and achieve the "Headshot" "Ghost Bullet" and "Exploding" enemy achievements in about an hour. Watch this YouTube video posted by kenberryfan83 to find the spot:
To achieve the melee kill achievements, NXEAchievementGlitch says:
"On the level Guts, Where you fight Vicus let the gladiator destroy all of the concrete barriors your team hide behind. Then kill Vicus as normal. When he is dead, dont change to Black just yet, change to Church and hold down the LT to use her sword on Vicus fat dead body. Everytime he moves to left and spasms that counts as a Melee kill. Tape down Lt and 30 mins late achievements unlocked"
The 50-250 kill achievements are the only ones that are of any difficulty. The others will just unlock as you progress through the game. A little tip, though, on the ones that you have to complete without dying: when you are about to die just switch to another character and if you do happen to die just press start and reload from the last checkpoint. You shouldn't have much trouble with the cheats enabled though. Just use Black and her exploding bullets throughout most of the game.