My non-spoiler thoughts on Firewatch:
Usually when I play a tight, short game like this, I want to be left feeling like I loved the world and want to play it again to spend more time in it. Take Undertale, for example. There was so much flavor to the world, it just left you feeling connected to it.
Firewatch very much didn't accomplish that for me. I just read a comment saying it was on-rails and I agree with that. After the QLEX I was left with the impression that there was a lot of exploring off the beaten path to do.maybe there is, but they don't give you a reason to find it. The pacing is such that going off the beaten path to maybe just explore doesn't make sense from an immersion standpoint. In order to get a more fully fleshed out world and explore more, you have to break from what your character would be doing.
Edit: game took me three hours going by Steam's clock. and it's not like I rushed through. Took my time, found some extra stuff, read notes, I wasn't speedrunning. I don't think there's much else there.
To sum it up, buy this game for 10 dollars during the Summer Steam sale. It's more suited to the game's atmosphere and it's a more worthy price point.