I sunk so many hours in Sims 2, you have no idea. Jumping from Sims 1 to 2 was a huge step up in quality and polish. You could have kids that inherited your genes! And they grew up! I plan to one day stream the 10 Generation Challenge just to see if I can get it done. I played Sims 3 and it was good, but missed the fun that 2 had. I liked being able to visit my neighbours finally but hated how they all grew up with you. Like, no, I am the word of God, I will say when these children become adults.
Another high contender is Portal. When I first played it, the I found the portal/wormhole mechanic to be some kind of ascended mechanic; it was beyond anything I would have ever thought of at the time. Plus the writing was so witty and well timed. Nothing feels out of place. It's like a perfect box of game.