I'll never forget the impact the first Shenmue had on me aesthetically (esp. the music, in a less internet-saturated/multicultural world). I turned more to 2, but came back to the 1 before 3 with the HD release.
In a word: while I'll always prefer 2, I noticed this time just how good the proportions of the original were/are. Two things stood out to me on that playthrough:
a. The excellence balance of content in relation to the size of the map
Gacha, move scrolls, leveling up moves, high scores (incl. slots), cassettes, the cat, little easter eggs with Nozomi-- with a map this small, there's always something you can do rather than progress in the plot, even if you don't want to do it. I always recognized this, but I think I appreciate it more in an era when open world focuses more on being open than a world. Even though I love exploring in 2, the "largeness" wears off once you've found it all. In 1, it feels compact in the right way.
b. A heightened sense of the amount of detail
Again, this was caught even as a teen, but the number of dialogues, the clever use of FREE music when his mood/the plot changes, the differing crunch sounds for how much snow you're running through-- while I think Suzuki is a perfectionist, I'm glad he was given this game to show that he's not just blowing smoke up our rears. Given infinite time/money, he'd make something wild.
(I'd mention some other things like characters, but I think 2 matched it almost as well on that front.)