Overview:
-Estimated achievement difficulty: 5/10
-Offline: 12 (200)
-Online: None
-Approximate amount of time to 200: 10-15 hours
-Minimum number of playthroughs needed: 8-9
-Number of missable achievements: None!
-Glitched achievements: None!
-Do cheat codes disable achievements?: No Cheats
Introduction
Getting every achievement in Rez HD will require some time and effort, but you won't have too much trouble. For starters, play the Xbox Live Arcade trial demo to get into the beat of the game. Once you get used to the controls, Rez HD is a fun game that is worth the money.
Step #1: Playing through the game
When you begin Rez HD, just play through each level normally to get the feel for the game. By simply beating the game, you'll get 5 achievements and unlock Beyond Mode which will allow you to complete score attacks for each stage.
Step #2: The Lost Area and Score Attack
After completing the game, go to Beyond Mode and play the newly unlocked 'Lost Area' level. Get a local ranking of 1st in the 'Lost Area' (150,000 points) to get the "The Forgotten" achievement. This is also a good time to get the "Ultimate Cracker" achievement in Score Attack by getting a local ranking of 1st on each stage. If you're having trouble getting a local ranking of 1st in these levels, see this thread.
Step #3: Laser Assassin and Firewall Buster
Even though the direct assault mode is unlocked, don't start playing it yet. First, follow the link that I just listed above, practice, and try getting at least 95% of the enemies shot down in each level for the "Laser Assassin" achievement. If you keep trying, you'll eventually get it. After getting the "Laser Assassin" achievement, you'll unlock Boss Rush. Get a local ranking of 1st in Boss Rush to unlock the "Firewall Buster" achievement. This unlocks infinite overdrives in Beyond Mode. Now comes the fun part.....
Step #4: Trance Hacker, Power Breaker, and The Rezident
To get "Trance Hacker", go to Beyond Mode, turn on 'infinite overdrives', and choose the highest form that you have unlocked. Now, play direct assault mode and start bashing the button. You'll be able to destroy everything in the game without even blinking. Direct assault is a non-stop playthrough of the game. It takes around 45-60 minutes to beat direct assault using this method. You need to beat direct assault, unlock the next variation of direct assault, beat that variation, and unlock more variations to reach the final direct assault variation. The final variation is trance. Beat this to get the "Trance Hacker" achievement.
Next, go to Score Attack and keep on beating the first stage until you get the "Power Breaker" achievement (Clear Score Attack 30 times). I estimated that it takes 5-8 minutes to clear the first stage. It is very boring to complete this stage 30 times. However, by the time you unlock "Power Breaker", you should have unlocked "The Rezident" for playing the game for at least 10 hours. If the achievement is not unlocked by then, go to the trance mission (Not direct assault trance) and leave the game on while you do something else.
[x360a would like to thank Axe Argonian for this Road Map]