Opus Magnum

I'm only 6 years late, but Zachtronics just doesn't miss with their games, and even in all these years, no one has managed to compete with the absoute brilliance that are their puzzle games. I completed Opus Magnum, and while it wasn't my favorite Zachtronics game, I sure as hell enjoyed it.

Opus Magnum is a game about assembling (or sometimes disassembling) compounds from atoms or other compounds. You have an infinite hexagonal grid, arms that can rotate, extend, and move along tracks to move these atoms and compounds around, as well as mechanisms for bonding, unbonding, and altering them.
As usual, there aren't a lot of different mechanics, but they work together very well to create interesting puzzles that have a lot of different solutions. In fact, as far as I know, it is not too difficult to create puzzles with just a single solution, but Zachtronics' games are good, largely because he consistently manages to leave the solutions up to the player's personal creativity.

The reason Opus Magnum is not my favorite from the series, is because the infinite boards give us too much freedom, and make the problems a bit too easy. Of course, having a low skill floor is not too big of an issue, because a big part of Zachtronics games has always been getting high scores on the leaderboards for making good solutions. Still, even in terms of going for high scores, some categories seemed more tedious to set up than difficult to come up with, such as minimal cost solutions, which usually just had one or two arms along some track, and very, very long lines of instructions stashing and retrieving pieces in elaborate ways to prevent collisions.
The appendix was actually space-constrained, and the journal offered more difficult puzzles, but they were not part of the main story, and thus not the bulk of the game.

Regardless of all that, I still heavily enjoyed Opus Magnum. Perhaps due to its lower difficulty, it is the highest rated Zachtronics game, so even if you don't think highly of your puzzle solving capabilities, it would probably be the best Zachtronics game to try, if you were going to try any. I would absolutely recommend it, and I hope to get around to playing the next game in not too long of a time.