At the main menu, select "Options", "Cheats", "Enter New Cheat", then enter one of the following codes to unlock the corresponding cheat option. If you entered the code correctly, a message will appear.

Always Slide - Press Green(2), Red(2), Yellow, Red, Yellow, Blue. This mode turns all guitar notes (not chords) into touch pad sliding notes connected by purple lines. It has no effect online. Note: This code prevents trophies from being earned.

Always Drum Fill - Press Red(3), Blue(2), Green(2), Yellow.

Auto Kick - Press Yellow, Green, Red, Blue(4), Red. This mode automatically plays the bass pedal for the drummer. It has no effect online. Note: This code prevents trophies from being earned.

Hyperguitar, Hyperbass, and Hyperdrums - Press Green, Blue, Red, Yellow(2), Red, Green(2).
Line 6 Effects - Press Green, Red, Yellow, Blue, Red, Yellow, Blue, Green to unlock additional Line 6 effects in the Music Studio.
Performance mode - Press Yellow(2), Blue, Red, Blue, Green, Red(2).
Metallica Costumes - Press Green, Red, Yellow, Blue(2), Yellow, Red, Green.
Invisible Rocker

Press Green, Red, Yellow(3), Blue(2), Green.
Air Instruments - Press Red(2), Blue, Yellow, Green(3), Yellow.
Black Highway - Press Yellow, Red, Green, Red, Green, Red(2), Blue.
Flame Color - Press Green, Red, Green, Blue, Red(2), Yellow, Blue.
Gem Color - Press Blue, Red(2), Green, Red, Green, Red, Yellow.
Star Color - Press Red(2), Yellow, Red, Blue, Red, Red, Blue.
Vocal Fireball - Press Red, Green(2), Yellow, Blue, Green, Yellow, Green.

Bonus characters - Successfully complete the indicated task in Career mode to unlock the corresponding character:

James Hetfield: Get 100 stars on vocals.
James Hetfield (Classic): Get 150 stars on vocals.
James Hetfield (Zombie): Get 200 stars on vocals.
King Diamond: Successfully complete the "Evil" song with any instrument.
Kirk Hammet: Get 100 stars on guitar.
Kirk Hammet (Classic): Get 150 stars on guitar.
Kirk Hammet (Zombie): Get 200 stars on guitar.
Lars Ulrich: Get 100 stars on drums.
Lars Ulrich (Classic): Get 150 stars on drums.
Lars Ulrich (Zombie): Get 200 stars on drums.
Lemmy: Successfully complete the "Ace Of Spades" song with any instrument.
Marcus Fretshreder: Get 55 stars on guitar.
Matty Cannz: Get 55 stars on drums.
Riki Lee: Get 55 stars on vocals.
Rob Trujillo: Get 100 stars on bass.
Rob Trujillo (Classic): Get 150 stars on bass.
Rob Trujillo (Zombie): Get 200 stars on bass.
Shirley Crowley: Get 55 stars on bass.
Zach Harmon: Get 100 stars in a band.
Zach Harmon (Classic): Get 150 stars in a band.
Zach Harmon (Zombie): Get 200 stars in a band.

Bonus instruments - Successfully complete the indicated task in Career mode to unlock the corresponding instrument:

Klown bass: Get 45 stars on bass.
Mean Green bass: Get 25 stars on bass.

Bonus songs - Successfully complete the indicated task in Career mode to unlock the corresponding song:

"Broken, Beat & Scarred": Successfully complete "The Thing That Should Not Be" song with any instrument.
"Cyanide": Successfully complete "The Thing That Should Not Be" song with any instrument.
"My Apocalypse": Successfully complete "The Thing That Should Not Be" song with any instrument.

Trophies - Successfully complete one of the following tasks to get a trophy:

The More I See (Bronze): Complete the Tutorials.
James Hetfield (Bronze): Complete the career as the vocalist.
Lars Ulrich (Bronze): Complete the career as the drummer.
Kirk Hammett (Bronze): Complete the career as the guitarist.
Robert Trujillo (Bronze): Complete the career as the bassist.
One (Bronze): Complete a song with any instrument on Hard or Expert in local Quickplay or Career.
Ride the Lightning (Bronze): All band members trigger star power simultaneously (4 player band).
2 X 4 (Bronze): Earn a band Hot Streak (4 player band).
The Struggle Within (Bronze): Complete a song in a band in Quickplay or Career (4 players).
The Four Horsemen (Bronze): Complete a song with all band members on expert in Quickplay or Career (4 player band).
Better Than You (Bronze): Win an online Pro Face-Off match.
Blitzkrieg (Bronze): Win an online Band v Band match (8 players).
Seek & Destroy (Bronze): Play 20 online matches.
The Unforgiven (Bronze): Win an online Face-Off match.
Reload (Bronze): Download a song from GHTunes.
Hero of the Day (Bronze): Complete a song on Expert + in Quickplay or Career (drums only).
Wherever I May Roam (Bronze): Complete a song in every venue.
The Memory Remains (Bronze): View a Metallifacts video.
Metallica (Silver): Complete any instrument career on Expert (Guitar, Bass, Vocals, Drums or Band).
...And Justice for All (Silver): Earn 100 stars in Band Career or any single instrument Career.
The Ecstacy of Gold (Silver): Earn $15,000.
Metal Militia (Silver): 100% a song (4 player band).
Nothing Else Matters (Silver): Complete the career in a band (2-4 player band).
Holier Than Thou (Gold): Complete all instrument careers.
Platinum Artist (Platinum): Earn all of the Bronze, Silver and Gold Trophies in Guitar Hero Metallica.

Additionally, there are 26 secret trophies:

Damage Inc. (Bronze): Perform as the drummer.
Motorbreath (Bronze): Perform as the vocalist.
Invisible Kid (Bronze): Perform as the bassist.
Some Kind of Monster (Bronze): Perform as the guitarist.
Master of Puppets (Bronze): Earn the highest individual score on a song in a band (4 player band).
Black (Bronze): Win an online battle match with the Fade to Black power up.
The Unforgiven II (Bronze): Win an online Face-Off match by 25,000 points or more.
The Unforgiven III (Bronze): Win an online Pro Face-Off match by 25,000 points or more.
Cure (Bronze): Recover from a poor performance in Quickplay or Career.
Disposable Heroes (Bronze): Create a new custom rocker.
Blackened (Bronze): Create a new custom tattoo.
Eye of the Beholder (Bronze): Create a new custom band logo.
Fixxxer (Bronze): Create a new custom instrument (guitar, drums, mic).
The House Jack Built (Bronze): Complete a song in every In-the-Round venue.
Trapped Under Ice (Bronze): Complete a song at the Ice Cave venue.
Stone Dead Forever (Bronze): Complete a song at The Stone venue.
King Diamond (Bronze): Rock out as King Diamond.
Lemmy (Bronze): Rock out as Lemmy.
Astronomy (Bronze): Hit every star phrase in the song Orion.
Green Hell (Silver): Drum every green note and finish the song Blood and Thunder with the rock meter in green.
Creeping Death (Silver): Score 575,000 on the song Creeping Death as the guitarist.
Dyer's Eve (Silver): Score 450,000 on the song Dyer's Eve as the drummer.
Fight Fire with Fire (Silver): Score 340,000 on the song Fight Fire with Fire as the bassist.
Stone Cold Crazy (Silver): Score 65,000 on the song Stone Cold Crazy as the vocalist.
Enter Sandman (Silver): Score 330,000 on the song Enter Sandman on guitar.
Battery (Silver): Score 1,000,000 on the song Battery as a band (4 players).