For RTS I felt like Medieval: Total War was less repetitive than Rome: Total War. The main reason being was that in Rome: Total War, you only had 2 potential Super Powers, the Egyptians, and then the Romans, while all the other factions predictably get swallowed by the two.
Whereas in Medieval: Total War, everytime I start a new game, any country could become the dominant Super Power, and each experience is unique and unpredictable.
So in short, I think a game is less repetitive if it's unpredictable. If Splinter Cell changed the patrol patterns and locations of its guards each time you replay a level for example, then the game becomes less repetitive (you rely less on just brute memorization, but on pure skill, which I think is the ultimate test of stealth).
Do I like random level generators? No. But they do spice up your replay.
