I played Inconsiderate Climbers with my brothers the other day and had a blast. I really liked the slow discovery of both the mechanics and the social constructs in the game.
Mechanics: We didn't initially realise that the various machines were doing a specific thing; we thought random stuff was just happening all the time. Once we realised the machines were doing something, it became a lot more interesting because you had incentives to use someone else's machine, or block them from using a machine. We also had a discovery moment of how to use the arrows.
Socially, we started trying to block each other from getting points, but eventually evolved into a more cooperative environment, once we established the idea that you're not trying to be the first to win, just trying to win, therefore it's OK to let others get their points as long as you aren't hurting yourself, and they might reciprocate.
It brings up an interesting thought about the whole "non zero-sum game": it's more of a mindset than a mechanical difference (it's only "non-zero-sum" because it says it is). Technically, basketball could be said to be a "non zero-sum game" since scoring a goal gives you points without deducting points from your opponent. It's only "zero sum" because you "lose" if you have fewer points than your opponent. IC looks like any other race to the top until you get a mindset of "it's OK for the other players to get points, I'm just trying to win myself," and then that opens up the entire social game (not just pure selfishness). I guess the problem is, that concept is only really communicated in-game by what happens when somebody wins (the game continues). Before I see that life goes on after somebody wins, I feel an intrinsic need to be selfish. I'm not sure how the game would best communicate that.
It's also not clear what some of the machines do, even after a lot of play. Some seem fairly random (is the 3-white-balls machine literally just "do 3 random effects"?) And some of the "disasters" seem unavoidable. The beams of light sometimes fill up the entire screen, and the rising water similarly can sometimes go all the way to the top, drowning everyone. I think those disasters should be less lethal.
I like how the different machine goals effectively give players different personalities. If you've got the lightning machine, then you're trying to hurt people and I've got a natural incentive to stop you. If you've got the heart machine, you're just trying to keep yourself alive, but you're also in natural competition with everyone else who also wants those precious hearts.
The next-level arrows are particularly good design, requiring some degree of collaboration between players. I like how N-1 players can collaborate to thwart anybody's machine activation by simply agreeing to move onto the next level before they can get to the machine.
Sound effects would definitely be good. It feels weird to play a totally silent video game.
I'm not sure the game has particular longevity. I feel like we've sufficiently explored the mechanics and there doesn't seem to be anything left to discover. Perhaps there could be some different "levels" with different machines or layouts, similar to how a racing game has different tracks.