Pacing and tension are functions of plot. And the fact that an author might not have an outlined a plot before writing doesn't change the impact of the plot as a reader.
There are all kinds of things you can do to influence pacing and tension during a session without having a plot. I routinely use all of them. If I know, as a GM, that there's a vampire near the PCs, for example, then I can drop all kinds of hints, foreshadowing and other things to ratchet up the tension, and draw out the session so that the encounter, when it happens, is appropriate dramatic.
Sure, the PCs could say screw it; I don't want to fight a vampire! and leave, in which case my effort came to naught, but again, that's the risk that you take if you value player agency. Mostly, they don't do that, IME. But that doesn't have anything to do with plot at all.
My thesis is that a pre-published adventure can either tell a story (to be "like a novel or movie"), or it can set up the pieces to allow the players to construct their own story. To me, you appeared to be asserting that this isn't a binary, and that adventures can do both. I'm simply confused as to what aspects of "like a novel" are preserved if "plotted" is removed.
In addition to what I said above, but not meant to be comprehensive:
- interesting characters with quirks, personality and motivations
- interesting villains with plots in place that they're executing, regardless of what the PCs are or aren't doing, which have a noticeable impact on the setting around them, especially if they don't take steps to try and thwart them.
- premises that are more interesting than "there's some rooms over here. There might be stuff in them."
- opportunities to develop relationships between characters (PC on PC, PC on NPC, etc.) that have some depth and interesting meaning. I don't mean by fiat; "my sister is in my backstory" but because of interactions that happen in game
- intrigue and skullduggery happening below the surface. If PCs ignore the clues, then they end up with a much more straightforward game, and don't even recognize the machinations of movers and shakers around them, but if they do, then suddenly the whole thing starts to resemble The Godfather.
Not a single one of those requires plotting, and yet it creates an experience that is much more like a novel or ongoing serial TV show, or something like that than the "default" way of playing the game as its presented. Again, it's not
exactly like a novel, because that
would require plotting and railroading to accomplish. But in my experience, trad players don't actually want those things. They want to have an immersive experience that keeps them entertained by utilizing skills borrowed from storytelling mediums to give them a much more entertaining experience, but one in which they can actively interact and influence what's going on, and they feel like they have meaningful agency at all times.
