"Wait, the game is already over?"

I don't know if repeated play throughs count, but I'll go for Sonic R. Once you know the stages well enough (about the same time you've perfected the lyrics you're singing along-

we all need, to work together
to build a better life, to make it what we feel
we have to make it real)

then you can unlock all the hidden extras and best the games 2 endings (with emeralds; without em) in about half an hour, without any sort of difficulty.

It's a shame because it seems like so much effort went into crafting the intricate stages, but in the end the major shortcuts just ended up extremely over effective and most of the routes through the stages become pointless.

Jam it back in, in the dark.