To me Shenmue is just a timeless game that doesn't seem to age like other games did and still do.
It was THAT special when it came out. So much that it's still something unique to this day. The attention to detail is so incredible for a game made in the last century. It goes beyond the limits of the graphics itself. The music is also extremely strong and timeless. The free music is just pure magic!
The freedom in the game may not be able to rival todays sandbox games but Shenmue is an action adventure and for that genre it still delivers an incredible amount of ways for the player to spend time with it.
Above all else it's the characters and the story that stand the test of time. The facial animations and the voice acting have aged but the characters are still very believable and just extremely likeable. It might be slow, it may seem boring and it will take a bit of time to get into, but once you reached a certain point you'll just get sucked in this incredible experience.
The game just had a huge impact on me when I played it the first time back in 2000. Like described above it took a bit of time until I got sucked into the vortex of it's magic but then I absolutely fell in love with it. Over time it never got old. On the contrary! I still to this day discover new things, find new ways to enjoy the game and fall in love with it deeper and deeper. It's almost to the point that you could talk about "possesShen". Yeah I know, terrible pun.