I don’t think this is quite a complete response to Rowan’s position but, in the interest of “other things that are responsive and RPGs or RPG adjacent” -
Disco Elysium, arguably, does the “choices matter” thing as well as Mass Effect does - the “overall plot” is the same, regardless (you’re not going to discover a different killer or anything), but a number of your choices significantly colour both the way that unfolds to the extent of you finishing the game with an entirely different partner, if you get Kim killed, and the same “personal version of your Detective” level of choice importance that many people here are noting is signally important about how ME reflects on “their Shepard”.
I’d argue that this is easier for DE, since it’s both a shorter game - although not by that much, given that the “average completion time” for DE is “20 to 30” and ME is “17 to 30” depending on how many extras you do - but it’s also got a lot less fancy expensive assets (relative to the period in which it was produced).
(One of my beefs with Kentucky Route Zero, conversely, is that it doesn’t seem to do this. Sure, you can pick different choices for your viewpoint character’s responses to things… but even if you never pick any of Conway’s dialogue options that suggest he’s an alcoholic… he still is one, when it becomes narratively important. )
Indeed, I’d argue that there’s quite a few pieces of Interactive Fiction and IF-adjacent games which also manage to significantly include choice in their narrative - 80 Days springs to mind here - with all kinds of unusual branches possible and covered (despite the decreasing likelihood of each being discovered by a particular player)… again, because the cost of doing so is much lower than in AAA game which needs to be fully voice acted, animated etc etc etc.
(It’s also worth considering the converse solution to needing “reactivity” to all choices: simply not having an overarching narrative! The Crusader Kings games - and especially 2 and 3 - are all effectively strongly choice-based RPGs of a kind, and the reason they can give you all the freedom they do is of course that they don’t have a strongly crafted story.)