Well - I decided I'd give it a third and final go because honestly, after serious thought, your work deserved me to at least finish it after getting this far and how good the quality of the actual game was overall. I ended up finishing it with minimal hints moving forward.
After the rock wall, the puzzles got a bit better again - here's some final thoughts for you.
--- Awesome Final Puzzles -----
The polearm puzzle was actually very, very good and I love how it takes ideas from Shadowgate and expands upon then to actually make certain un-useful things useful ;) - i'm sure you know exactly what I mean.
One of my favorite puzzles in the game honestly was the lamp puzzle. I really like those types where the answer that seems obvious is always wrong and you have to think about how you, as a person, would introduce another factor into the obstacle you are facing. Fantastic touch on that one.
The last puzzle was really neat too - I liked how you made us think about the resources available to us and that many of them can have certain uses in the given situation. One thought on this - maybe some sort of message that the intended effect took place to reach it. I thought I crashed the game the first time I triggered it.
Lastly - love the direct homage to Uninvited (will always love that game even if the puzzle system was abysmal for the sole fact that the ghost lady scared the living crap out of me when I was like 8 XD). That was hilarious and yet (plus, the extra surprise if you do the wrong thing is both awesome and suggestive if you are really paying attention and examining the things you find).
---Puzzles I think Need Work---
The Xspot puzzle was a little odd I will admit - not sure where you would have known to apply that one outside of an educated guess. Once I knew where it was used, it was very logical once translated through earlier hints, but If there was a hint as to where to begin, I missed it.
The grey key - probably would have benefitted from more area hints. Accessing what you need is pretty obscure and again, no hints are given until you examine the correct pixels. A nudge would have been useful here.
The Gold/Silver puzzle - After using a hint it sort of made sense, but there just wasn't enough guidance or hints that I found. I knew the general gist of what the thing was, but I don't think I would have ever known what to do to determine the answer without a slight hint.
Overall, the majority of the puzzles were pretty good it seems. There were a handful that did not make sense as i've specified previously, but as others have suggested in other comments, an in-game hint system that may give secondary, vague clues for these situations may completely fix that problem. Or, perhaps additional clues written in are necessary in the form of a better Exam system. It was far too limited in this game - no question. You're the developer, so i'll leave that to you - just thoughts on my end.
BUT, after playing through in it's entirety, I think it's fair to give the game a slightly upgraded review based on everything in total. It still isn't the caliber of puzzle structure of Infested, but it's not awful as a whole and as I said originally - with some fine tuning on your puzzle structure, your third game is gonna be an absolute smash (and I surely hope you sell it this time - we've benefitted enough from your time for free :) )
------ Final Scores ------------
The game looks, sounds and functions amazingly. These things cannot be overlooked. While puzzle structure is more important than anything (and Infested hit the bulls-eye with this one), these things are important too.
One other thing - as amazing as the soundtrack is (and I loved it, please don't get me wrong) - Infested preserves the ICOM experience even further with the 8-bit music (another absolute gem). Taking both of these into account:
Infested - 10/10
Spectable - 8.5/10
Take care and thanks again for listening to my feedback.