The Anno series is a bit hard to pidgeonhole. It's got elements of SimCity, bits that feel like an RTS, and complex resource management rivaling a Railroad Tycoon or Tropico game. I haven't played many of the mobile sim games that have been popular of late, but I have to imagine that there are some similarities and parallels there as well.
Anno 2070 is the most recent entry in the series, but I've been playing the previous games off and on for years. It's a solid strategy experience, although it's not without its rough edges.
The Anno series centers around building island cities and attracting large populations to live there. As you build housing, citizens move in. Each house holds a certain number of citizens, and the number of citizens per house increases as their "level" increases. Leveling your houses requires that you fully meet the demands of your citizens, and at each level they demand more goods. At first, your citizens might demand tea and fish, but before leveling up they'll also want a special entertainment building. After they level, they'll demand more buildings and more goods.
You supply these goods via manufacturing chains. At first they are simple - creating tea only requires a single 'tea house' building, surrounded by three tea fields. However, as you progress, this chain grows longer. Creating tools, a common building material, requires that you mine iron and coal ores. Then you must smelt the iron ore and coal ore at another building to make iron. Then you must process the iron into tools at still another building.
Many of these buildings require a certain number of fields around them in order to operate at peak efficiency, and the radius around the building where you can place these fields is limited. Further, the goods have to be carted around the map through a system of depots, warehouses, and roads. Organizing your buildings to maximize your production per tile is a central part of the game's strategy.
Have I mentioned yet that each island is of limited size, and you can't produce every good at every island? Settling multiple islands and creating efficient shipping and production routes is essential. You've got to ensure that your settlements are capable of producing the goods your citizens require, and settle new islands strategically in order to ensure you're capable of meeting new demand. Building ships and setting up trade routes ensures that goods move from the place they are produced to the place where they are consumed in an efficient manner.
All of this is pretty standard for an Anno game, however. Anno 2070 adds a few new twists. The game takes place in the near future, instead of the "age of sail" in previous titles. Global warming has reduced the amount of land available, and this makes island settlement a viable strategy for exploiting natural resources. Since we're in the near future, things like submarines and aerial drones also feature prominently. The names of buildings and goods have changed somewhat, but the overall balance has remained more or less the same.
In the previous game, Dawn of Discovery (or Anno 1404, depending on your region), there were two "races" that had different building types, citizen types, and requirements. Unlike in most RTS titles, where you picked one race or another to play with from the start of the game, you essentially had to play both at once. The two races were co-dependent - in order to reach the highest level of development you'd need islands settled with both citizens, as there were things that could only be produced by one that were essential to the other, and vice versa.
Anno 2070 has three total "races" - the Ecos, the Tycoons, and the Techs. Typically you pick either the Ecos or Tycoons to start with, and then you unlock the other two as the game progresses. The Ecos and Tycoons are essentially caricatures of environmentalists and capitalists. There's no interdependence between them, and building an empire of both isn't typically required or even a scenario goal. Their goals are typically obvious, shallow, and one dimensional.
The Techs are the odd one out, as they're mostly for support - they can research technologies that benefit either of the other two groups. They're also the only race that can settle underwater, which makes them more akin to the Arabics in 1404, who could settle desert islands. They have fewer buildings, requirements, and citizen levels than the other two, and I don't believe I ever started out as them.
Previous Anno games pivoted their economies around your gold balance. Taxing your citizens generates revenue, but providing for their needs creates cost. Producing enough to meet demand and still keep the gold flowing is an important factor in success. Anno 2070 adds a couple of other wrinkles to this - power and ecobalance. Power is required to run most every building, but it costs money and may impact your ecobalance. Ecobalance measures the amount of pollution you generate via production. Certain buildings (which cost money and power to operate) can offset your pollution and increase the ecobalance. A negative ecobalance on an island is bad for growing crops and makes your citizens less satisfied, so they pay less in taxes. Balancing cashflow, power, and the ecology of your islands is yet another key to success.
Taken all together, this creates a complex system that requires a steady hand to maintain. Say you want to advance your citizens to the next level. You build a production chain to satisfy one of their new needs, and this requires you to settle a new island. This new island needs building materials and a trade route to take the products back to your town. Now your citizens are about to advance. This requires building materials, and as they advance the number of citizens in your town increases. This puts a strain on your food supply, so then you build some more fisheries. Well, that put you over your power budget, so plop down a few more power generators. Now the ecobalance is negative, and everything on the island is producing less. More ecobalance buildings (which require more power - hope you planned ahead!) need to be built. Eventually, you reach equilibrium again and you can take a breather for a minute. Whew! Now it's time to repeat the process...
Things get hectic, and there's a lot to manage at once. This management can be a burden, sometimes for no good reason. There's a really complicated set of formulas involved in producing most goods. For instance, one iron ore mine might be enough to supply 1.25 iron smelters. Also, the ecobalance of an island can effect the efficiency of your myriad farms, which adds a bunch of modifiers to these formulas. This means you're almost constantly stockpiling or bottlenecked by some stage of the pipeline. The game doesn't do a very good job of showing you these trends in an easy to consume fashion.
Keeping track of the dozens of goods and their stock levels is also a pain. You can look at a warehouse and get sort of a high-level "is the stock on this island going up or down?" picture, but things like trade routes and multi-island production break this feature. Most of the time I found myself trying to maintain a mental count of how things were going, and checking every so often to ensure needs were being properly met.
Some of the game's features aren't fully explained by the tutorial or the in-game, either. For instance, setting minimum quantities to leave on an island when configuring a trade route is important, but never explained. Similarly, it's possible to speed up game time if you're waiting for things to be produced or for a game event to occur. Luckily, they were mainly features I remembered how to use from previous games. I'd hate to be a new player jumping in at this point though - there's a lot to absorb and not very much hand-holding going on.
War, diplomacy, and combat have always been a bit awkward in the Anno series. 2070 "solves" this by basically gutting it. There's some ship to ship combat, and air units, but the emphasis is definitely on building rather than destroying. Whether or not this is a good thing is up for debate, but personally I didn't really play Anno games for their RTS/combat elements, so having them more or less removed is fine by me.
The campaign is another casualty, though. Previous games had a long campaign that spanned dozens of missions, but this game is over in around 10 or so. There's more "online" or "global" elements, such as short 3-mission campaigns that are time-dependent, and a few scenarios to play, but it really feels like the single player/offline elements have been given the axe, and that makes me sad.
Speaking of online, there's a sort of career progression system in place here, along with global "elections" where players can vote on various things that provide small benefits to everyone's game. I didn't find any of this to be particularly essential, as the effects were relatively tiny and I felt like I had very little control over what they were.
Overall, Anno 2070 is an addicting strategy experience that sadly suffers from several missteps. It's a bit overly complex in areas, while being blatantly oversimiplified in others. The online elements take some of the focus away from the single player campaign, and that's disappointing. I'd still recommend picking it up on sale, though, especially if you're a fan of the Sim or Tycoon series. It's a unique game in a series known for being unique, and that's saying something.