That is not exactly subtle nor needs much figuring. Them trying to kill you is game telling you they are bad in very straightforward way.
That kind of scripted event, and environmental story-telling, was extremely novel in a FPS game back then.
It's easy to nowadays handwave that away as merely "Marines shoot player, player realizes Marines are enemy" like that kind of heavy scripting is just something mundane. But back then it wasn't mundane, it was quite revolutionary.
Before that the norm in the genre was mostly maze shooters with very limited NPC interactions, like certain Doom enemies fighting each other or some wall or another blowing up in Quake, Half-Life took all of that and brought it to a whole new level.
Back then, half life was one of the games that made me think about how linear games are evolving to be. At one place, you could decide to go left or right and it joined back together quickly. It was straightforwardly prescripted, which is something we discussed with friends a lot.
I did not needed hindsight of years and my current experience. If anything now I have less experience as I spend significantly less time playing games like this.
a) Choosing which enemies to go and kill with your chosen color of pixel burst.
or
b) Choosing which set of text and vaguely representational spritework the game would expose to you.
Many "linear" games offer tactical rather than strategic freedom. There is a sort of conservation of experiential depth, limited by the players' ability/inclination to absorb new interaction concepts, and the availability of developer resources to build them.
This is a good way to put it IMO. Command and Conquer is an interesting exception in the action genre because it had some meta strategy in branching missions of the over world.
Half life was not one of them. At the time, they were games that allows more strategizing and more tactic and more micro choices. Half life was as prescribed as it gets.
yes here's a clip of someone saving the scientist: https://youtu.be/e_l84_7jDoU?t=163
And the difference between full cit scene and what happened in half life was really really minor.
The difference between a cut scene and embodying a character while things happen around you isn't a minor thing for many of us.
Half life was part of pattern of moving towards extremely linear. It had better graphics than normal at the time. It had attempt at actual story. It was not move toward more agency to the player nor toward subtlety.
It had less choices than normal at the time, not even in terms of whether to hide on left or right, less options for tactical decisions, less of anything like that.
In terms of showing rather then telling via text, almost anything has that aspect.
Half life had very good graphics for the time. That is where it shined.
Wolfenstein and Doom have literally zero story choices of any kind. Not even inconsequential ones!
Clearly, Half-Life has superior story telling to Wolfenstein or Doom. Not by much, can be argued, but it clearly does. And at the time, the little bit felt like a whole lot compared to literally nothing.
In wolfesrwin, you could at least go back and had choice between left or right doors. Half life had only way to go - forward. It was like sitting on train moving on railroad.
Maybe you just missed them all!
Just off the top of my head from the start of the game: Activating the alarm from the button on the reception desk, getting the guard into trouble. Going into the kitchen and playing with the microwave cassarole (referenced from later sequel!). Opening lockers in the locker room (looking at people's stuff), getting the hazard suit and heading back (if you try to proceed without suit, guard will tell you to go get it - nonlinear maps!). Pressing the broken elevator button, sending people plummeting. Opening the dumpster to find the hiding scientist. Operating vending machines.
Did Wolfenstein or Doom have anything like this? In Wolfenstein you can optionally open cells and find hidden doors behind walls. In Doom you can push buttons, and you are always required to do so to proceed.