To me, the ideal is for the main game and end game to be related, but not identical. Some good examples:
Pyramid: What is the word? vs. What is the idea?
Musical Chairs: Choose the next line vs. know the next line, or Choose the next line from 3 choices vs. Place the lines in order.
Bruce Forsyth's Hot Streak: High scores in the main game come from guessing what words your teammates hadn't already used; win the main game by guessing what words they will come up with.
I don't usually like shows where the two parts are completely different, but when the end game just feels like the solo version of the main game, it feels like an end game for the sake of an end game. (See: Wheel.)