I am working hard on puzzles right now. We've had figured out, for a while, the basic set of locations you can travel to on the island, and what the puzzles are in each. These locations were defined to varying degrees of specificity, though. Sometimes we know what the puzzles are, exactly (they are all designed and implemented) but aren't sure what the architecture is. Sometimes I have concrete ideas for some puzzles but only vague ideas for other puzzles, and it's a case of "I will fill these in later on, when I have time to think about it and come up with something good here; but it is pretty clear to me that there will be something good here, so I am not worrying too much about it."
Eventually, these things have to be figured out. Over the past month or so we've done some of that figuring. We nailed down the architecture for a couple of areas (including the all-important area where the player starts the game). We've done this in a way where the architecture and the puzzle ideas have synergy, which is always nice. In particular, there was one location that, from the beginning of development, was basically a big box with a window cut into it and some puzzles stuffed inside. For a long time (maybe 2 years!) I was never sure what to do with it, but eventually the architects suggested an idea for that location. I mocked it up and didn't like it. They suggested another one. This one sparked an idea for how to make the structural properties resonate with the puzzle theme, and when I built even just a rough-draft of the building, I found the result to be strong. Lately we've been finalizing that location too.
So anyway, there are all these spots on the island that represented vague ideas, with puzzles there that were just in rough form, or that weren't even implemented fully, but just served as reminders to do something there. I've been going through and filling in a bunch of those.
I have also been working with some other puzzles, which seemed "done enough to ship", and thinking hard about how to make them better. Braid benefited from a lot of this kind of attention -- a lot of games would have shipped with just early versions of the puzzles in that game, considering them to be just fine; but the more I worked with the puzzles in Braid, the more I found better, simpler, more-to-the-point versions of them. The same thing is happening here (though The Witness is a much bigger, more-complicated game, so sometimes it is challenging to get to that same kind of clarity.)
With regard to the visuals (modeling and texturing), things have been coming along nicely as well. Pretty soon a high-profile game magazine will publish some screenshots of one of the most-finished areas of the game, showing the look we are targeting and giving a strong hint of what the game will be like stylistically. When the magazine is out there we will link it here.
(This has not been a particularly coherent update; just wanted to let you all know what is up!)