Qual é a melhor maneira de tornar um jogo viciante (por horas)?

Possibilidade de recuperar a vida.
Não muito difícil, mas muito fácil.
Personalização da velocidade do jogo.
Humor.
Atualizações online que deixam o jogo evoluir.
Livre, excepto no caso de certas actualizações.
Carga rápida.
Multiplayer.
O jogo faz parte de uma saga.

Exemplo com quase tudo isso:

Plantas vs, Zombies 2 (para Android):
https://play.google.com/store/apps/details?id=com.ea.game.pvz2_row&hl=es_419

Plantas vs, Zombies 2 (para iOS):
https://itunes.apple.com/ve/app/plants-vs.-zombies-2/id597986893?mt=8

Dino Run (online-flash):
http://pixeljam.com/dinorun/index2.html

Bloons Tower Defense 5 (online-flash):
http://ninjakiwi.com/Games/Tower-Defense/Play/Bloons-Tower-Defense-5.html

Bloons Tower Defense 4 (online-flash):
http://ninjakiwi.com/Games/Tower-Defense/Play/Bloons-Tower-Defense-4.html

>p>Bloons Tower Defense 3 (online-flash):
http://ninjakiwi.com/Games/Tower-Defense/Bloons-Tower-Defense-3.html>p>Bloons Tower Defense 2 (online-flash):
http://ninjakiwi.com/Games/Tower-Defense/Bloons-Tower-Defense-2.html

Bloons Tower Defense (online-flash):
http://ninjakiwi.com/Games/Tower-Defense/Bloons-Tower-Defense.html

Mude & Blood 2 (online-flash):
http://www.kongregate.com/games/urbz/mud-and-blood-2.

Mude & Blood 2 (zip):
http://www.mudandblood.net/downloads/mnb2.zip

Warfare 1917 (online-flash):
http://armorgames.com/play/2267/warfare-1917

Robokill (online-flash):
http://www.rocksolidarcade.com/games/robokill/

Robokill 2 (online-flash):
http://www.rocksolidarcade.com/games/robokill2/