(the other big reason is that so many of the planets had extremely bland maps).
This is my main gripe on the series (that 3D might address somewhat!).
Even if it was unpolished there was a real charm to random environmental puzzles and platforming that revealed secret areas and treasure.
It's just cool to go back to the world after the story was done with it and find new rewards.
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SuperNiceDog - 1, pjbasis - 0