Game time: 15-30 minutes.
Recommended player count: 1 or 2
I've played Onirim several times solo and twice coop. It's better coop than it is solo, though it's fantastic both ways.
Many reviews state that the reviewer didn't try coop because it didn't look fun or because the coop rules looked "tacked on." I think the game is very well-designed to scale from 1 to 2 players, but it's even better when played coop with limited information-sharing. You have to pay attention to your partner's planning and strategy if you want to succeed, much like in Hanabi.
It's a lovely, challenging game, though I do tend to win more often than I lose so far. I expect the same to be true when we continue to play coop. My wife and I both enjoyed it, and she wants to keep playing.
It's easy to become enamored fairly quickly. I haven't tried every expansion combination yet, but I've tried each of the four expansions in the first edition separately and I strongly regret not seeking out the second edition which comes with five more expansions, since each expansion has changed the gameplay notably without lessening the fun.
Onirim is very portable, but it needs a lot of table space unless you don't mind seeing what cards you already discarded (which I personally find to be necessary for strategic decision-making, particularly coop.) I would never play this on an airplane, but I will probably ALWAYS take it with me when traveling, for the hotel rooms and host houses.
Despite this, it's not *very* complex. I can imagine some players growing bored of it, though this would likely be due to short-sightedness or having a personal preference for complex mechanisms (which is certainly fine.) The base game is too simple for me to continue forever without adding one of the built-in expansion decks. I can't stand simple games like Settlers of Catan, but I expect to play Onirim hundreds of times, which is why I need to find a copy of the second edition. If I plan to play it for years, I might as well add as much variety as I can. Several players claim the expansions in the first edition are the best ones anyway, so maybe it doesn't matter.
It has art and a theme and it's very pretty but not immersive. It certainly sets a mood though. I believe my wife hardly noticed.
I believe this is one of the essential games for a couple to own, especially a couple that includes someone who is willing to play solo. I thought I would never be the sort to care to play a game solo, preferring video games for that, but Onirim, Space Hulk, and Draugr changed my mind. It's even better for parents (or other couples who often only have short times to play in) because it's short while still containing hard decisions, a variety of ways to mitigate the randomness in the deck, cooperation, and fun but simple mechanics.
8/10, will never remove from my collection.