I've still been a bit conflicted, because the game has always seemed a bit vacuous. These days I tend to prefer games with thematic focus. Tzolk'in's physical presentation is very cool, and both the art and the gears use authentic Mayan imagery. Somebody obviously did some research. It's just not clear whether this is all just flash, or if it informs the actual game systems in any way.
The subtitle of the game is "The Mayan Calendar", and Tzolk'in appropriately does seem to revolve around time and tempo. The goal is to score lots of points, which you do by gaining the favor of the gods, installing crystal skulls in Chichen Itza, and building buildings. The resources you'll use to do these things are wood, stone, gold, and food. Acquiring those resources and then turning them into points involves making efficient use of your workers, who you will commit to various tasks for various lengths of time.
Tzolk'in looks a bit like a worker-placement game, because there are workers and you place them. But it's not, at least not in the traditional sense. Here, you have 5 different cities you can assign workers to, each of which specializes in a different task (Palenque does farming, Yaxchiclan resource gathering, Tikal building & technology, Uxmal trading, and Chichen Itza crystal skull mounting). Each turn you must either place one or more workers onto the cities' starting spots on the moving gears, or remove one or more workers and do the action for the space they have advanced to. After everyone has taken a turn the big central gear rotates, driving all the other city gears and advancing all the workers on them by one spot. Crucially, you can't pass. If all your workers are on the board, you have to activate one or more of them. If none of your workers are on the board, you have to place one or more. Placing more than one worker has an increasing cost in food, the currency of the game. You can never be blocked from placing a worker in a city, but if someone else is already there you have to pay more food to get in (although you'll start on an already-advanced spot).
So, it's a game about timing. At some of the cities (resources, food, and skull-mounting), staying on the track longer is usually better, so you'd prefer to keep your worker riding for as long as possible. There are enough exceptions to the general rule that it's not really a rule – for example, some spaces are forests that need to be cleared (for wood) before they can be farmed (for food), and some technology makes early spaces very efficient – but it holds generally. Other tracks are not as straightforward. On the building & technology track, you might want either building, or technology, and those spaces are disjoint and spread out across the dial. The trade track is a true grab brag, with a focus on the third spot which gives you another worker. It all rewards planning. When you jump on a track, you'll want to know what you plan to get out of it (say, you need at least 4 corn, or the space with two technology advances). But you also want to be able to be flexible, letting a worker ride if an opportunity arises. Fortunately, you can always take an action you've already passed by (for a cost in food), so it doesn't always require extreme precision.
Less obviously from this description, but more crucial in practice, is that the requirement to always either place or activate a worker makes it important to find a rhythm. Most of the time you want as many of your workers as possible riding the gears, moving towards better action spots. Maybe you'll want one or two workers on long-term tasks, while the rest cycle on and off of shorter-duration ones. As long as you can keep productively placing and removing workers a few at a time, your costs stay low and you're getting a good number of advances every time the gears rotate. As soon as you have to activate or place larger numbers of workers, you take a hit: 4 workers are extremely expensive to place all in one go, and even 3 aren't cheap, but workers off the board aren't working. You want to maximize the amount of time your workers are being productive. My first few games I won comfortably by simply focusing on efficiently keeping my workers working cheaply and not worrying too much about where the points were ultimately going to come from.
Tzolk'in is a no-randomness, 100% open-information game and this juggling act is obviously a bit complicated. Also, it's a CGE game, so the rules are somewhat involved – lots of different action spaces, different buildings, technology advantages, temple tracks with different payoffs, and so on. You could easily imagine this bogging down into total analysis paralysis as Dungeon Lords or Shipyard so easily can. But while it's unquestionably a detailed and thinky game, the gears don't seem to lock up, or at least not as much as you might guess. I think it's because you operate with a lot of constraints – you'll never have enough workers or enough food to do what you really want to do. If you're short food, which you often will be, there is nothing for it but to go to Palenque. With only 5 spots to put workers, the game focusses on giving you a limited number of highly distinct, high-leverage actions and there is very little of the micromanagement that so often weighs games down.
The big scoring opportunities in the game come from 3 major sources: Monuments you can build, which provide familiar endgame bonuses for having done a range of things during the game (advanced tech tracks, built specific kinds of buildings, farmed, and so on); getting Crystal Skulls and placing them in Chichen Itza; advancing in the temples; and to lesser extent, building buildings. Temple advancement is fairly diffuse and there are opportunities to do this, usually at the cost of resources, on all three of the non-resource-gathering gears. Advances on the temple tracks also feed back and give you resource bonuses twice a game. Crystal Skulls are the most focussed: there is exactly one spot on the resource gear that gives you a Skull and only a Skull, and these are useful only for mounting in Chichen Itza, which gives you points and a bump in one of the temples (and Chichen Itza does nothing else). The rest of the resources are quite flexible, being used for buildings, monuments, buying technology (which makes action spaces more productive), sacrificing to the gods, and selling for food. The net effect feels fairly well-balanced. There aren't any strategic cul-de-sacs, it's easy to feel like you're making progress, and scores will tend to be close. Unlike a lot of 100% open-information, no-luck games, this is not a game designed to make you feel like an idiot.
Even though Tzolk'in plays smoothly and feels pretty elegant once you get into the groove, there are still a fair number of details here and it's moderately tedious to have to explain the game to new players (I haven't even mentioned a fair amount of detail). So the question inevitably arises: what is it all in service of? That's the question that nags at me.
I think the answer is, it's in service of itself. Tzolk'in is thematic in the same way that Ra is thematic. Ra is an auction game with nice art and nods to the familiar Egyptian tropes: floods, pyramids, gods with funny heads, and so on. Tzolk'in is a game about scheduling and timing with nice art and nods to less-familiar Mayan tropes: calendars, corn, step pyramids, even their (as postulated by Jared Diamond) deforestation problem. Does Tzolk'in grab on to anything fundamental about Mayans, their calendar, or their civilization? Not really, and I guess my instinct is that for a game of its complexity, it should.
Ultimately I think my instincts are wrong in this case, though. Tzolk'in is a very playable, engaging, meaty euro that gives you lots of planning and resource optimization opportunities without many of the hazards that usually come with this class of games: systemic imbalance, reliance on brute-force analysis, downtime, effective player elimination. Worker placement games can be especially problematic, since they rely on figuring out how "hot" various action spaces are which requires you figure out not only what each space is worth to you, but what it is worth to every other player. This contention for spaces is a very limited element in Tzolk'in, and you virtually never have to do this sort of analytical heavy lifting. Another nice feature is that Tzolk'in is only minimally about infrastructure development, so early choices don't weigh particularly heavily and it's about making good choices for the whole game. Tzolk'in feels tight, moves at a good pace, and while it presents you with interesting tactical and strategic choices, it doesn't require or reward excessive forward-looking analysis at the expense of strategic judgement.
Tzok'in is definitely quite different in texture from the first generation of euros – it's not as mechanically tight, has a much broader canvas of options, and is quite complicated by 1995-2005 standards. However, the core elements do feel a lot like these classics: focussed, with tight pacing, good balance, and nicely presented. Because I found the gear gimmick distracting, it took me a little bit to understand that was what Tzolk'in was. Once I figured it out, I quite enjoyed it.