Anytime during the single-player game, press the right bumper and back buttons at the same time to pause the game and enter a hidden 3D stage-viewer. Left thumbstick tilts and rotates the view, right thumbstick zooms in and out and pans left and right, and the triggers raise and lower the field of vision.
Cheat Effect
RB + Back Enter 3D Stage Viewer

Geometry Wars 2 Unlockables
Achievements

Complete each achievement to get the allotted gamerscore.
Unlockable How to Unlock
Unlocked All Modes (25) Unlock all game modes.
Magpie (15) Collect 500 geoms in a single game.
Millionaire (15) Score at least 1,000,000 points in all single player modes.
Phobia (15) Score 1,000 points in Waves without collecting any geoms.
Slalom (15) Chain together 5 gates in 5 seconds. Crossing at least one gate every second.
Surf (15) Dodge 8 lines of enemies in Waves without firing a shot, or destroying any enemies.
Treaty (15) Activate 30 zones in King without firing a shot, or destroying any enemies.
Rebound (15) Destroy 75 enemies in a game of Deadline using bullets bounced off of gates.
Wax On (15) Rub your ship along all four arena walls in Pacifism.
Wax Off (15) Perform the Wax On achievement twice in a single game, don't forget to breathe.
Game Over (15) Reach the end of sequence.
Smile (25) 2, 4, 11, 15, 17, 18 and 19.