In this case "dated" pretty much means "handholding". All of the "modern innovations" that shenmue is missing is just stuff to make the games easier or more mindless.
Having a map with waypoints and quest markers, tutorial levels, dialogue options, some random person in your ears/head telling yo what to do, etc is all stuff we've grown accustomed to, but really don't make for a better experience.
The beauty of shenmue is that it's the first and really the only game in which what to do next is all organic. You have to explore the world and pay attention to your surroundings to progress, and on the flip side you can spend hours doing your own thing not progressing the story at all, and that's enjoyable too.
It's a really unique gaming experience, and pretty much an exact opposite to what modern gaming has become.
All innovation could be referred to as "hand holding" then.
The reality is, a lot of people are not interested in being completely lost in a huge environment, or have to restart their play through because they haven't played in a couple weeks and forgot where they left off.
I'm a huge fan of the game so a majority of my criticism comes from bitterness of how long they have taken to keep this story alive, and also knowing that the story won't be concluded for another couple releases.
For me...when I talk about this particular game feeling dated, I mean specifically in terms of animation, voice acting, overall presentation, and pacing.
As games (the entire entertainment medium) have progressed, a lot of the "padding" or "fluff" has been removed for a more streamlined experience that gets to the "point" a lot faster than the games of yesterday.
I'm cautious with this series because of how long it has taken, and the fact that Yakuza is such a similar game yet is not very widely received in The US.
I would be surprised if people that are not familiar with the Shenmue series at all, pick this up for the first time and really enjoy it. Especially if they had played a game like Yakuza Kiwami/0/ or 6 before ever playing a Shenmue game.