Top level:
Action
Adventure
Strategy

Action:
3D Shooter
Action-Adventure
Arcade
Fighting
Open World
Platformer
Racing (Arcade-style)
Rhythm
Shmup
Sidescroller
Stealth
Vehicle Simulation

3D Shooter:
FPS
Tactical
Third-Person Shooter

Vehicle Simulation:
Combat Flight
Flight
Motorcycle
Naval Combat
Off-Road
Racing (Sim-style)
Railroad
Ship
Space Combat

Adventure:
Action-RPG
Conventional Adventure
RPG
Survival Horror

Strategy:
4X
City Building
Economic
God Game
Puzzle
Real-Time Tactical
RTS
Theme Park
Tower Defense
Transportation
Turn-Based Strategy
Turn-Based Tactical

Remove
2D (just delete it)
DOTA (merge into Tower Defense)
MMO (covered by Play Style)