Any, good, lengthy iPad games?

Most games you find on the app store tend to be quick throwaway games with little to no reason to revisit them after their short completion time. Does anyone have any recommendation as to a good lengthy game, I’m not talking AAA length here (although there length is getting shorter and shorter) but just something worthy of my money. I have and enjoy:
Plants vs Zombies
Fieldrunners
Mirrors Edge (Completed but enjoyed)
Thanks in advance guys and gals :D