There will be spoilers for the game and the DLC in my text and the comments
If you don’t want to be spoiled, play the game first, it’s a really really nice game that’s best when discovered
My favourite moment for the game (as for most players), was when I fetched the Warp Core and had to go to the Nomai Ship. The music made my heart beat so much, and the trip seemed so friggin long.
But my best discovery within the game is understanding how simply turning off the flashlight would be enough to make the quantum objects move. It was so satisfying discovering it for the first time.
EoTE
That was pretty cool to discover, but I at first thought I could only apply it to pillars I could sit the lamp down on. I had to look up how to progress with the final puzzle, and only then did I realise I could place the lamp on the ground. I think it was the whole having to look practically straight down that really got me.