I do wonder what the playtime will be, but ultimately, I think that it should be irrelevant to expectations, personally. As you've alluded to, bigger/more isn't necessarily better and can actually hurt an experience-- it's about quality, charm, and perfection, not quantity, IMO. I'd go a step further and say that 4 hours was the perfect length for Super Metroid, not just in the context of its time but as a game overall, and that it would be misguided to expect/demand "more" from that in today's age, because "more" alone isn't meaningful in any way. One could argue that Hollow Knight is overly long and too big for its own good.
I've always vehemently disagreed with the way that people like to treat videogames as an "occupy my time and distract me from my life for x amount of hours" service in general. Personally, I want a perfect and appropriate experience, however short or long that takes, and I'm paying for that finely honed appropriateness and craft, not novelty or time investment. The fact that good things can potentially take up a sizeable chunk of time is a necessary evil, not the actual reward that is worth paying for, IMO. I've seen 15 minute games that I've admired and would pay more for than 100 hour games, personally.
We should give games passes for being short not because they're old or because they're indie, but rather because it should be irrelevant to how good they may or may not be, IMO. If lack of length coincides with lack of substance, the latter is what's actually important to focus on, and the perceived correlation between the two is mostly a complete fabrication, IMO.