How long should a game be?

I played 10000000 on the iPad this weekend (where it costs $ 2 instead of the PC version on Steam for $ 4), a match three puzzle dungeon running game with retro graphics. I got the required score of over ten million to reach freedom in under 5 hours. There is an endless mode after that, and on the iPad you can reset 10000000 by uninstalling and reinstalling to restart from scratch. But for all practical purposes I got a 5-hour game for $ 2. And I was thinking that this was good. I probably s

World of Warkraft...