I'm surprised no one has mentioned Kerbal Space Program. KSP is an open-ended game where you build your own rockets and launch them from a low-gravity planet populated by amusing alien species who much resemble the Muppets' Beaker. Real spaceship structural simulation and orbital mechanics is the focus of the game. Even on the free demo version one can work up to landing a Kerbal on the "Mun", and maybe even get him back to Planet Kerbin.
Many videos of KSP, both instructional and destructional are available on YouTube. (Making absurd rockets and blowing them up is half the fun.)
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"Reeling and Writhing, of course, to begin with," the Mock Turtle replied...-- Lewis Carroll
I would say that its replayability is not as high as some of the games in this thread (say, Agricola or Dominion), but you will definitely get a number of games out of it. DD9 really enjoys it, and I do too, so I think it stays age-appropriate for a long time. 
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