Hi Nathan, long-time Myst and Riven (Riven being the masterpiece in my view) player here. Think this is solid as a very early prototype, in that things work and nothing is broken. I think you should get it to a better stage though before showing it to someone whose feedback you REALLY value (like in the games industry or anything). I would say get at least one of the following in place before that:
1. Story. Obviously this is lacking apart from the fact that there is some nasty rain and that you have a hazmat suit
2. Graphics. I know it's a sketch, but given it's a small world perhaps there's scope to get them really good before making it bigger.
3. Puzzle integration into world. This somewhat ties into 1. The puzzles are fairly logical in that they are self-consistent but still feel a bit "this is a puzzle sitting here randomly in a world". They're not really connected to this world. For example, the colour one makes sense and I guess it meant I gave power to that bridge so it could raise. But I don't really get why anything in the world would be set up like that. Why would there be a bridge (that also conveniently blocks access to the input for the second puzzle) that is controlled by a three-colour combination lock? And why would there be a 'combination lock' for clearing the sky of acid rain?
All up, as a rapid prototype it's pretty good that it all basically "works" and there's a good level of "I must have tried everything... oh no, wait, you can walk down here".
I don't know if the acid-fear could be kept up the entire game if you made it bigger. It is damn annoying in a way, but perhaps that is the central mechanic you're going for (find a way out of the rain). And I liked the fact you could go underwater, but also only temporarily.
On thing just in the way this demo is set up. It's actually easier to kill yourself in several cases than it is to take the time to walk back to re-enter a code. Might not want that to be something players use to move faster as I doubt that's the intent. Although I must say that if everything had have reset every time I died I would have quit immediately and stopped playing. I did play this through to the end.