I'm not sure where this "unfolding of atmosphere" comes from, given that, as I said, most of the game takes place in sewers and destroyed houses with poor level detail even for the game's time.
"Poor detail"? Really? I know I'm at least four or five years behind the curve technologically, but as I played through the game, a lot of what I saw was impressing me even by what I understand to be
today's standards. It's true that the Source Engine back then didn't support some of the newer, more advanced graphical effects, but I found the sheer amount of everyday physical objects scattered throughout the appropriate environments to be almost staggering at times. You'd walk into an abandoned house and see all of the little accouterments that you'd expect to. And thanks to the still-ridiculously-awesome physics implementation and the gravity gun, there was all kinds of goofy stuff you could do with them. Not to mention the facial-expressions feature that Valve implemented, which as far as I can tell was just about unprecedented at the time.
Thing is, someone mentioned talking to the . . . zap guy on the boat. But why would I do that??? Don't I have **** to do? places to go?? I shouldn't have to intentionally break the flow of the game just to learn information I should already know. For example, at the start of the game, in the train station, okay people sitting around, I'll go talk to them. Later on, I'm running the gauntlet, the police are after me, there's no time for chit chat. So why as Freeman, would I take 10 minutes to talk to the guy on the boat when time is of the essence??
Isn't the golden rule of gaming to hit up every NPC possible, no matter what you're "supposed" to be doing at the moment? Or is that just me?

I definitely need to agree with CP here. I found the first sewers to be very repetitive, and I never really knew what I was supposed to be doing.
Ex. Run!
... where?
...
See, I feel like the repetition worked for those segments. This wasn't something like the original Halo, which seemed to prescribe to the design philosophy of, "Hey, let's re-use this same room in this big alien structure twenty times, because it's
alien." Sewers are...well...sewers; they're not going to be ridiculously varied in appearance just for the hell of it. At that point in the game, you had just been cast off on your own, forced to fight your way through to another (seemingly) safe haven. Having to blunder your way through the sewer's twists and turns kind of reinforced that in-character emotion for me.
I do understand that the game might not have worked for some people, but it did work even better than I could have hoped for me. And given the amount of mid-90s scores that it received at the time and the lasting praise it's garnered, it obviously worked extremely well for a whole bunch of other people too.