It was a years-long campagn of 3.5e D&D, and I don't know if it worked as a "good finale" but here's what I learned.
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Take your time. The finale can stretch for 3-5 sessions - you've earned it, so be as indulgent (for yourself and the other players!) as you want.
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Think about what the players actually care about. Don't feel the need to bring in all of your secret lore that was never revealed - give them a scenario that touches on their flags and brings them together!
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Don't sweat the loose ends. It's ok if not literally everything is resolved. It's time to end this thing. Give them a fireworks show, let them hit their big character beats, and say goodbye.
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Don't be afraid to swing big. It's now or never! You're not coming back to this game, so blow it up if you want! And don't hoard this freedom for yourself - give your players the power to change the world on as big a scale as they want.
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Have fun. It doesn't have to be perfect. You and your friends have worked for months (probably years!) to get to this point. Think about all of the memories you made together. Those are the thing you will keep after this is all done. At the end of the day, the finale is just another game like the dozens you've played before. It might not measure up to the highest highs of the whole campaign, and that's ok, it doesn't have to. This is a celebration. Enjoy yourselves. You did it.