Super Metroid

 https://www.youtube.com/watch?v=Wlu5Mx-9wwU

Even with the limitations of the SNES, back in 1994 Nintendo created what has to be one of the greatest endings ever made, and the number one entry here. The final battle with Mother Brain is just so brilliant. The battle itself is tricky, but when Mother Brain drains Samus almost to death, only for the young Metroid encountered earlier to rush in to Samus' rescue, in turn giving Samus a super-powered laser beam, you couldn't help but sit there, almost falling off your seat. With Mother Brain destroyed by this beam, which was amazingly satisfying with each head-whipping blast, the whole planet is set to blow and Samus has a very short time to escape. It's a mad rush to her ship, with the planet exploding around her.
Once off the planet, it explodes, then the game ranks players, and depending on how well you did, you'd see a slightly different ending, with the best rating showing Samus in a bathing suit.
What makes this ending so impressive is the amount of impact it has, even when using such limited tech. The final battle blends in perfectly with the ongoing story of the last Metroid in captivity, which sees Samus as a mother figure, and the seamless transition to evacuating the planet produces an adrenaline-pumping finale. Arguably, the actual ending is the rating and congratulations screens, but here Nintendo does what many new games fail to do. It puts you in control of the whole ending, making a final boss fight so much more. Pure brilliance.