What is depth of gameplay and what is just repetition?

[MrPopo]

Depth is when there are things to discover/utilize that take time to figure out. A good example would be the original Quake. At first it's just running through and shooting dudes, which is a fun but shallow game. But then you discover how you can utilize explosions to make jumps or just generally traverse the level in ways you didn't see before. Now you get to start figuring out risk/reward on when you want to put yourself in danger to get to places.