Or, reusing level scenery but with different level contents. Inspired by Zelda the Master Quest, which is kind of Zelda the Ocarina of Time with ''remixed'' dungeons. I haven''t played Z:TM, but the idea is that it has different puzzles to those in the original, the dungeon layout is the same, but you will have to take a different path through the dungeon.. because the objects in the level are different (ie. switches are in different places, etc.) It does this through the use of re-occurring elements such as pressure switches etc.) As long as your gameplay supports it, this may be a fun idea. ie. you complete the level, the evil wizard casts a spell -says get out of here alive! if you can.. he vanishes. You turn and see that the level has changed completely..

A lot of racing games let you do that, actually.

In games that are less pulse-pounding, though, it has to be well-executed to keep the player from thinking "What a cheap way to make the level longer." Proceed with caution.

MANY games do this already.