Negilahn does not present itself as a puzzle Age. It looks like a sort of wildlife observation blind. You are restricted to a spherical metal pod, with windows looking out over a vast jungle. Sets of buttons control spotlights and audio speakers. And near the Negilahn linking book, there's a sheet of paper describing various Negilahn animals.
So this strongly implies that you can attract different animals with different combinations of light and sound. Time of day may also be relevant -- Negilahn has a day-night cycle, as some Ages do. (If I sound uncertain, it's because most of what players know has been discovered by experiment over the past two days! There's no manual in the game.)
Attracting animals is puzzle-like; we want to figure it out. But it's not a traditional Myst puzzle. For a start, it's non-deterministic. Nothing is guaranteed to attract a particular animal. In fact, it's possible that some players' Negilahn instances have more wildlife than others. (It's also possible that this is a false hypothesis. As I said, people are still experimenting.) There may be a seasonal component as well as day and night -- which would mean that it's a long-term challenge: some animals might be hard to find until weeks or months from now. And there's also no reward except wildlife-spotting. There is no particular notion of "solving" Negilahn; you can keep an animal checklist, but that's all.
Negilahn offers a second reward, which (seems to be!) independent of the wildlife (and of the lights and speakers and all.) I will not spoil that.
So it appears that Cyan is expanding on the social and experimental aspects of Uru. Social, because it would take one person a very long time to learn anything about Negilahn. The Age's responses are slow and probabilistic. You need a lot of people collaborating to make progress. But it's not a multiplayer Age in the sense of the two recent ones: once the player community discovers something, you can read it and enjoy the benefit on your own.
(But, on the third hand: Recall the hypothesis that some players have more wildlife, or different wildlife, than others. If that's true, then Negilahn would be social in a third way: players who have access to particular animals would want to invite other players in to see them.)
I should also mention an element of Uru which is not ideal, but which is unlikely to go away: out-of-band information. Which is to say, peeking at the game data files.
The software doesn't try to encrypt the data folder. This means that, for example, I knew on the 28th that Negilahn would open up the next day -- a whole lot of files were downloaded with "negilahn" in the name. And I know the name of the next Age to open, because it was downloaded in the Feb 28th update as well.
You can't load up an entire Age data file for viewing -- at least, I haven't heard of anyone succeeding at that. But you can play individual audio files (Uru uses Ogg audio), and peek at chart displays and so on. This is particularly relevant to Negilahn, because someone found a file describing the conditions for attracting particular animals! (I'm not sure if this chart is still in the game data -- it was found several weeks ago, before the update.)
That was either a major spoiler, or a major boost to the player research effort, depending on how you look at it. It doesn't seem to have been a complete "solution"; perhaps it was intended to be just enough to get started on. Either way, this chart was certainly intended to be released to players eventually -- it wouldn't have been in the game files otherwise. It's a case of finding something early, not looking at internal game mechanisms.
But this sort of thing will happen again, so it's worth mentioning.
Finally: the community response to Negilahn.
What's become clear -- and I'm not saying this as a criticism of particular players, or even of players in general -- is that it's hard to internalize the notion of an open-ended, experimental game. Every time Cyan adds a new type of Age, a great cry arises from players who were expecting something else, and who are disappointed with what they got.
I saw it happen with Negilahn; I saw it happen with the multiplayer Ages; I saw it happen with the "Path of the Shell" single-player game in 2004. Heck, I saw it with the original Uru Ages which require kicking objects around -- and there I was one of the people crying out in disappointment. (I wasn't that thrilled with the "Path of the Shell" gimmick, either, come to mention it.)
I don't want to focus too much on the complaints. I mention them because, if you go to the forums at any given time, you are likely to find someone saying "This is awful; this is a cheat; if this is what Uru is like, I'm cancelling." Don't panic, is all I'm saying. It's not the entire Uru community saying that. It's just that complaints are inherently noisier than contentment.
Again, I am not criticizing these complaints. Some players are genuinely disappointed with any given release. In the case of Negilahn, very few animals have been spotted. All my speculations above about how the wildlife could work are just that -- speculation. It takes only a little less optimism to decide that, sorry, Negilahn just doesn't have much to offer.
I have suggestions for both sides here.
I think Cyan needs to do a better job of -- well, of managing expectations, if that doesn't sound too cynical. Negilahn (I'm assuming) offers a long-term process of zoological discovery. It should have been presented as an observation Age with a nice view of some jungle, plus the possibility of long-term discovery. The DRC could have said (in-character): "Look, we don't know what wildlife there is, or how often it appears. We have some ideas about the ecological relations of certain species. We haven't had time to find out more. You go and see what you can find out."
(Yes, that sneaks in a subtle hint that patience is required. I insert that with hindsight, because a lot of the Negilahn discussion has centered around whether players want to wait to see things -- both in the sense of waiting for an hour at a window, and waiting for a month as seasons change. But as long as I'm second-guessing Cyan, I might as well second-guess well...)
Cyan does play the DRC as ignorant about some things, and that's good. (The second reward that I mentioned is entirely outside the DRC's awareness.) But they aren't playing up the "We're exploring, you're exploring, we're both in this together, we'd like your help" aspect of the game.
The other aspect Cyan could improve is their variety. The January and February releases were both multiplayer Ages, with nearly identical puzzles. That's great if you like solving that particular puzzle with a group. But if you aren't into multiplayer work, that's two months without anything you care about. Now we have an observation-pod Age, and the web site previews imply that the next release will be another one. So anyone dissatisfied right now has more dissatisfaction to look forward too. If Cyan was mixing things up more, I think the community would be happier overall.
At the same time, I wish more players would take a step back and say -- okay -- I don't like this. (Whatever "this" is.) Every new Age annoys somebody, and this month it's my turn. Next month (or two months from now) it'll be someone else's turn.
Uru is, as I said years ago, the puzzle-equivalent of a short story collection. Each one (or maybe each pair) is going to try something new and different. Inevitably, you're going to hit one you dislike. Try to see what it is, think how you'd have done it better, and wait for the next one. That's all.