DOOM II. Sinking the final rocket into the demon's brain on L30 Icon of Sin. I did it before Z-axis engines like ZDoom. 30 years ago? Something like that.

The very last level is worthy. You must train in order to finish it. I could not do it today without a month or two of practice.
These days if I want that rush, I boot up DOOM 2016 and play the first level on Ultra-Nightmare Arcade.
I did enjoy killing every last Brotherhood of Steel member in the airbase and then blowing up the Institute in FO4. That wasn't a rush, it was a culmination of about 800 hours. I was done. Kill em all now.
More recently, the first time I killed the final boss in Risk of Rain 2 was quite satisfying. Took about 3 months.