I've been playing games on the iPad as well, they are fun but 70% of the games are simple minded games, and the other 30% although well thought out and done, don't hold a candle to high priority games on something like the 3DS or Vita.
iPad is a good source for your all around schedule/life with some fun games attached, but it will never, or at least not for a very very long time replace actual handheld gaming devices.
Don't get me wrong, though, I've been addicted to that Temple Run game for like a week, it's fun to game on for quick 10-15 minute bursts.
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