Look at it this way. A player downloads Jewel quest and aargon. They play for an hr of jewel quest and they look at the in game map and see that they've only played 10-20% of the game. So they think to themselves.. if I buy this I'll get another 80% more. If they like the game that can seem like good value for money. Also they're thinking.. I'd like to get to the mysterious temple, and I wonder what the last level is.. and so on. In aargon there's no map, but there's tons of levels. If you like solving the puzzles you could play for an hr and not scratch the surface. That will feel like good value for the money. People want to know that when they put out their 20$ they're going to have more "Stuff" to do. Things to collect, awards to win, etc.. Whatever it happens to be. But also keep in mind that if people basically dont find the gameplay fun none of this will help. This is all to motivate the player to do more of what they do level to level. They have to actually like the swapping of gems or whatever it is. Otherwise it might just seem like 80% more pain. So adding a map or goals isnt going to necessarily fix a game. But it can help.