At Spielwarenmesse 2017, designer Hjalmar Hach gave me a runthrough of the game (video here), but a brief runthrough doesn't give you a good feeling of how the game actually plays out. You can understand the gist of things — collect light with your trees in order to plant and grow new trees, eventually harvesting them for points — without understanding how mean this game can be. It's the most pacific mean game I've played in years. Everything about the graphic design is inviting and joyous, yet you're all meant to embody cruel nature, block everyone else from the light, and see them shrivel to nothing in the forest while you reign as the oakest with the mostest.
That's the hope anyway. Sometimes, of course, you're the one doing the shriveling, especially since you can block yourself as easily as others. In some ways, though, you have to block yourself, just as you block yourself in your regular non-tree life as a human, taking on more responsibility than you should or agreeing to a project that you know you'll regret or just wanting to do more than you'll ever have the time for (which is a common refrain in the Martin household come convention time).
If you're going to be at Gen Con 50, you can check out Photosynthesis yourself at the Blue Orange Games booth. I hear that they're offering a discount for those who cosplay as an sycamore, but that might have been something I made up right now.