I played on the middle/normal difficulty. And, yeah, I engaged with the crafting tech tree system somewhat because I like those kinds of systems, but also because your manual said I should start early, so I did (but, then ended up upgrading the wrong thing early and rarely having spares of the resource I needed to actually craft as I said :). Maybe I would have enjoyed the hardest difficulty more if it forced me to / caused me to have time to craft =). This difficulty felt about the right length, though (maybe spent about 1.5 hours).
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Ah yeah that sounds about right, It could do with a complete tuning pass to potentially make the materials a little more abundent on the middle and lower difficulties.
By starting early you were at least able to get through all the upgrades, which is great. I'm not sure how long a playthough on the hardest difficulty would be for someone playing for the first time - but it could easily be 2.5 - 3 hours I think (far too long I know). But then crafting probably gets better, at the expense of the rest of the game.