ambivalent.
Most of the "length" is from the game's logistical model. If you hide, you don't use your bits but the Alien is more likely to find you.
If you use your bits, you progress an exponential amount faster, but then you run the risk of teh Aliems wrecking your shit later on through overuse amping up the statemachine.
I've played twice, neither on anything other than hard, but everyone I've talked to who had played medium or easy have pretty much finished within 10 hours by hiding or about 7-8 hours by using gear. a 60% drop in time spent is a pretty big deal, though the same would have been said of Halo's legendary mode.
Also the length is given by essentially using every story-theme the universe has presented... again, so after Marlowe you're pretty much playing a variation on a theme within an already given theme.
The game is atmospheric and fun enough to justify the contextual padding, but it's still pretty clearly padding, especially when shown against the DLC and Survival.
I predicted that people would overhype this simply based on FINALLY getting a non shitty Alien game from the current vendor, and I think >most< of the hype is deserved, it's still kinda fitting that line, honestly the replay value for anyone other than a rabid fan is low.
So whilst people here would hazard ARMARGAR I WIL PLAY FOR AL TEH TIMES EVERY TIME 4EVARS, I'm pretty sure in average gaming circles this game will simply be a super polished mobile monster closet you play once and move on, and maybe come back to every chunk of years if nostalgia and time permit.