Simon Christiansen's work has been characterised by brilliant concepts that are ultimately let down in the execution. The execution has improved considerably (and so have the concepts, really); the overall experience, though, is still a little rough.
The big concept of PataNoir is that similes occupy their own adjacent reality that you can manipulate: change the simile, change the real world. One frequently-employed subset of this involves altering the personalities of people. Elements of one simile can be used to tinker with another, and in some sequences similes are gates that allow you to plunge into entirely separate worlds. There are, then, a number of distinct kinds of manipulation that can be performed with similes, and they're thrown at you pretty much all at once, together with rules about how the system works (similes can be used to modify real-world things, but can't act directly on them: a simile key will not unlock a real door.) When I first played it I had a little trouble taking on everything at once, and stalled out perhaps halfway in.
The simile hook provides a good deal of rather lovely imagery (kicking in good and early), with elements of fantastic journey about it; to film this you'd want Terry Gilliam (or Švankmajer, though it's not quite that dark). There is a hauntingly dark atmosphere to much of it. Not every section is quite as spectacular as it could be: the climactic scene in particular could be richer and darker. But there are many images I took away from this: (Spoiler - click to show)the angel fountain encircled by snake-paths, the sleeping giant, the eyes you swim into like subterranean lakes, the plunge from bottles on a table in a messy apartment into a minaret-studded city. There's much here of the raw stuff of imagination, the pure delight of strange transformations.
Structurally, the game has areas you can travel between, and you will fairly often need to travel back and forth. The game's natural pace is a sort of Anchorhead-like, leisurely poking around at things; but I ended up speeding things up with the walkthrough a good deal, for a couple of reasons. Dream or hallucination is a flow state: it's not something where you get hung up on a fair-but-difficult conundrum for a while and have to work through it logically. The play experience matches up much better with the experience-as-written when you cheat. Simile-logic isn't really consistent enough for a Savoir-Faire simulationist approach, and there's often a whiff of read-author's-mind about the solutions. In the impossible-to-make Platonic ideal of this game, more or less everything you tried would advance the plot somehow. That said, going to the walkthrough really doesn't ruin the experience: it's still hauntingly strange.
Christiansen's biggest limiting factor remains narrative voice. This is exacerbated because of PataNoir's reliance on a genre that makes very strong demands on narrative voice, even when done as a pastiche. Noir needs a tone of slangy self-assurance, murky motives, a grimy, uncomfortable world full of implied sex, violence and desperation. PataNoir feels a bit more in Thin Man territory: there's a noir template, but it's being used in service to something else, it's as much a comedy on noir tropes as anything, and thus it's rendered nonthreatening. The characters are a little too straightforward: the obligatory femme fatale has the mandatory dangerous curves, but these are only significant as a simile: but the PC doesn't feel as though he regards her with either lust or trepidation.
And then there's the ending. (Spoiler - click to show)The protagonist, it turns out, has a rare mental-health condition ("Lytton-Chandler syndrome") and, off his meds, has likely fantasised the entire thing. A lot of people felt this was a cop-out; I'm not convinced of this, but I don't think it really matches up with the story as written. The tough, non-flowing puzzle structure isn't suggestive of hallucination, but of solid, graspable, permanent worlds; the contrast between the rich simile-worlds and the flat detective-noir story suggests that they genuinely do occupy separate worlds, rather than being elements of the same hallucination.
So ultimately I came out of this hoping that Christiansen would team up with a more confident wordsmith, or perhaps find something that allows him to develop his own voice rather than trying to replicate an established style.