In ZooSim, players compete to construct the most attractive zoo. The game consists of bidding and tile-laying. Every round consists of a closed-fist bidding for a zoo tile that depicts two animal displays, some paths and possibly some (0-4) trees. The highest bidder takes the tile and adds it to his or her zoo, then checks if the zoo now attracts any new visitors. These can come from other players' zoos or from the general supply. First five tiles are turned over and these are then sold one by one. After these five rounds there is a scoring round, players receive income and the game goes on with five new tiles being turned over. With each scoring, visitors are worth more points. After the fifth scoring, the game ends and scores are tallied. That's the rules in a nutshell.

Zoos can attract visitors for several reasons: having the most or second-most attractive animal display in a category (there are five categories of animals: apes, other mammals, birds, reptiles and sea animals), having the most or second-most trees in the zoo (visitors like to walk in the shade), and having paths that form loops (visitors don't like to backtrack their path around the zoo). If you put two animal displays from the same category next to each other, their values (displayed as a number of stars) may be added up to determine the total attraction value for that category. Trees are always added, they don't need to be on adjacent tiles.
Every loop simply brings one visitor to the zoo. A first place in any category (including trees) brings two visitors, a second place brings one. These visitors are continually moving along to other zoos if they have bigger, better, newer attractions - it's like an arms race.
The income players recieve after every scoring is one coin for every tile they have bought so far (the government supports the zoos based on their size).

As with every bidding game, carefully weighing up the pros and cons of each tile up for auction is important as you can only spend money once. Especially in the middle game money is extremely tight and winning a bid for a moderately useful tile, however cheaply, could mean you'll lose the bid for that very important tile later on.
The economy of the game is forgiving, however. Every tile you buy is more income later in the game. And since visitors becomes more valuable later on, it is possible to make a strong come-back in the later rounds. On the other hand, if a player manages to take an early lead in the number of tiles, his higher income may put him in such a strong position that it is hard to beat.
So far, I have not found this to be a big problem. Usually the players who buy less tiles have saved enough money to still be competitive. And if they continue to bid too low, they deserve to lose, right?
With fewer players, each player will acquire more tiles and that increases the possibility of creating loops. This increases the importance of loops in the end result, because the number of visitors available for first and second places remains the same. It has been claimed that simply building as much loops as possible (and picking up some second, maybe even first, places along the way) is a sure way to victory. This might be true in the two- and three-player game, but with four players (the way I have played most of my ZooSim games so far) it seems not strong enough. Until now, I haven't tried to play a loop-strategy. I thought about it a few times, bu every time I am drawn into the battles for majorities ("Darn! My shark is much cooler than your squid and I'm gonna prove it! "). It's good to keep an eye open for the possibility of building a loop, though.

The closed-fist bidding (with a very clever tie-break mechanism) makes the auctions go very quick, with the result that the game should be over after about 45 minutes. And that's if you play it at an easy pace! The production quality is great, especially when you consider the game is published by the author's own one-man-company. The pictures on the tiles (artwork by Frank Czarnetzki, a name I've never heard before) looks very good: It's bright, colourful and really cute. The visitors are black wooden puppets (a bit like the 'meeples' from Carcassonne). The 'coins' are wooden disks. Also very nice (although not very practical) are the "entry-houses" which are folded from thick card-board - they are also meant to hide your money behind.
The only problem some people have with the components is that is hard to track in what zoo the visitors from each category are. In a forum-discussion on a German site the author stated that he had tried with visitors in different colours but that he found that to be even worse - the visitors were camouflaged too well! A suggested fix was to paint a part of the visitors in the colours of the categories. So far, I haven't felt the need to do that.

I'm generally not a big fan of auction games, but this one is great! I suppose the fact that the auctions are so short helps a lot. Also the fact that it combines the auctions with a tile-laying mechanism is neat. There are no spectacular new mechanisms here but the game is well-rounded and very solid theme-wise.
Simple rules, tough decisions, relatively short game, extremely good looks and an appealing theme: this is not only a great game for avid gamers. Casual gamers and families should also like this one a lot.

Apart from the basic game I described above, there is also an "advanced game". Apparently the "advanced game" was the original design but it turned out to be very tough for beginners, with a high risk of player elimination.
In the advanced game, the game economy is more intuitive: income = # visitors - # tiles (revenue - costs), there are no points but the player with the most money at the end wins. If you can't pay the costs of your zoo, you're out of the game. I haven't tried this version yet but I hope I will soon, as it should provide a tougher challenge.