Really solid idea for a game - elements. The sheer database of knowledge in that part of science is astounding and yields many many ideas for a game. I'm glad you did this idea and not some other one where the elemental aspect of it is lost to the game mechanics. This one embraces it's science and it is a stronger game for it.
I really, honestly think this is 2 or 3 steps from outclassing "Cookie Clicker" and that is truly amazing as I never thought anyone would bother with the genre anymore (with Steam games being so cheap, browser games seem to be shortening).
However, you aren't quite there yet. I'm sure you know why and I'm sure what about to say is old, but I'm going to list off my personal cons with the game that make me take away a full star.
-Extractor bounce.
I don't quite understand why this is in the game. If it is to keep more than four extractors out of each element, then why not have a lock-in for extractors? Have the element divided up four ways and an extractor goes in each section. It would solve a lot of headaches.
-Lack of later depth.
You can expound this to mean endgame, or you can just infer "After Evolution" which is when I started to grow a little bored of the game. The game isn't meant to have my attention at all hours, I get that. That isn't the genre of the game. But after you start evolving (right around the third evolution if I'm not mistaken) the game starts to really die down in momentum. You start seeing the same Ammonia. Sulfur Dioxide, etc. And there isn't anything else to keep the player there or - more importantly - get him to return. There are better suggestions for improving this than I feel I could give so really consider them; especially if you want to release this to steam.
-Interface.
The UI is cumbersome as it stands. It is very cluttered, especially for a newcomer who hasn't played before. You're bombarded with tutorials and what have you that I didn't even know what I was doing until I realized I was actually in the game. Keep it simpler in the menus and this is mostly fixed, but even so I think the screen for the game is absurdly small. It feels like I'm playing Ultima again with my ol' 640x480 CRT. It would really help all the issues in this particular segment if I could get more screen real estate. I know you're probably avoiding leaving people out, but the vast majority have 720p or better at this point.
-Inteface 2.
Something important I felt to note that was due its own little spot in the interface is the lack of helpful tooltips. The tooltips that are there don't say much. Just a bit of wording issues that leads me to be a bit confused towards some of the upgrades, in particular the time spent renewing the atoms, or something like that. What does that mean? I just don't really get it even after I bought the upgrade once. Maybe I'm just an idiot.
-Background.
This is very personally based and I'm totally fine with you not even considering this, but the nebula background is very... bland, I guess. At least to me. It would be very nice if you had a few backgrounds to choose from as we'll be staring at it for a while, or have a slideshow-esque effect or maybe a slow panoramic view. Regardless, this is up to you - I just personally dislike the current background.
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All in all this is a very fun game at least to kill half an hour with. After that, some work is needed, but the potential is definitely there. I'd really consider some of the points I brought up before you even think about Steam, however.