Opus Pretty-Okay
Opus Magnum feels a bit like it carved a chunk out of SpaceChem, added one or two new ideas, and spent most of its development cycle trying to look pretty. (Like Shenzhen I/O did to TIS-100 before it.)
Where SpaceChem had chemical elements, Opus Magnum has alchemical elements. And where SpaceChem used traveling waldos to move atoms around, Opus Magnum uses arms, which can rotate or extend. (... But can also travel a path.) At least so far, there is no equivalent to SpaceChem's complex multi-factory problems. And the input/output sequence is locked, so there's no room for cleverly processing multiple jobs simultaneously; only one output at a time is allowed.
The gameplay focuses on different aspects of automation than SpaceChem did - at least to me, Opus Magnum feels more about micro-optimizations - but overall it seems simpler than its predecessor, which is a disappointment.
Also mildly disappointing is that the game's soundtrack frequently stutters and glitches. This really seems like the kind of thing that would have been ironed out in early access. EDIT: This appears to be a common problem in current Unity games.
The storytelling in Opus Magnum is a mechanical step forward for Zachtronics, if not a narrative one: there's actually a protagonist, with a name and a face. So where Shenzhen's emails or Infinifactory's NPC chatter felt like I was receiving flavorful directions, Opus Magnum really feels like it's telling me the story of Anataeus.
... That said, all the characters' dialog (including this protagonist's) is stiffly robotic, and their personalities are all pretty flat. The quality of the writing seems about on-par with SpaceChem's.
I will give some props to the built-in minigame, Sigmar's Garden, which is way less frustratingly obtuse than Shenzhen's solitaire game. It's still not all that engaging, but at least I don't actively hate it.
I'm definitely having fun with Opus Magnum, but I hope that later puzzles will find some more interesting high-level challenges for me.
Progress: almost done with Chapter II.