The interface is the next major point of issue for most new players. It's a very in-depth interface, but unless you look up how-to guides before/while playing, you'll find yourself struggling with the interface your first time playing. Movement around the game world is all controlled through the numpad, and the normal part of the keyboard is all your hotkeys for performing various actions. While it's hard to get used to for an RTS fan, soon you'll be micro-managing with the best of them. And micro-managing is what you'll have to do.
The third and final barrier to those wishing to enter into the world of Dwarf Fortress is starting out. It's an incredibly complicated system and, as such, requires you to know what you are doing if you want your fortress to survive your first winter. There are two ways to fix this issue. Either play your first year in several fortresses to get used to what you have to do first, or look up a guide that will help you get the beginnings of an economy going. Both are equally valid and equally fun ways, so it's really up to you which you wish to do. There's a lot of good guides on the Dwarf Fortress wiki, so there would be your first place to look in most cases.
When you first start a new game, a procedurally generated world is generated for you to play with. Everything from the course of rivers to the rise of civilizations is meticulously plotted and generated, making each world a much different place from the previous one. It also includes many biospheres in its simulation, so if you want to make a fortress in the middle of a desert or underwater, you can!
After your world has been generated, you must outfit your dwarves for the journey. You can either take a random sampling of items and skills (although you'll always have the essentials), or choose what skills and items you will have. It is highly advised that you choose what skills you need and what items you want manually, because otherwise you end up with useless skills on your dwarves, such as soap-making.
Upon reaching your fortress site, you will need to carve tunnels and rooms out of the mountain. You must take into account sound, ease of use, defensibility, and various other attributes when both choosing your location and starting your construction. For example, building a Carpenter next to a bedroom will keep the dwarves in the bedroom up with the noise, making them upset. You must also take into account the Z axis, as you can dig both upwards and downwards into new levels, making your fortress a complicated 3D base of operations.
On top of all this, each dwarf is independent and has at least a modicum of free will. Sometimes things you want done will get done immediately, other times it'll take weeks. The dwarves also have moods and thoughts, which leads to one of the biggest killer of dwarves: dwarven depression. You have to juggle keeping them happy and keeping the fortress productive in order to survive, and it's a fairly hard task. They are also sometimes stricken by strange moods, which leads them to produce the incredibly valuable artifacts.
After a fortress is lost to the annals of time, you can either start over completely (including a new world), or start a new fortress a few years after the old one was lost. If you are particularly daring, you can even try to reclaim the old fortress with your starting crew. As it usually becomes a base for one of the evil races, though, this is a fairly hard task.
On top of all this RTS simulation, the developer also added a rogue-like RPG system that is both seen in normal play and in its own game mode, Adventurer. Dwarves and adventurers can wear different clothing and armor, become proficient in different skills, and take on various different enemies. Adventurers can also take quests and hirelings to help them in their escapades as well. Everything involving the Adventurer mode is very in-depth and interesting, although not as polished as Fortress mode. The locati0onal damage is the most interesting part, allowing you to sever limbs and such in the heat of battle. Just be careful as the enemy can do the same to you.
In the end, Dwarf Fortress is a game all about making your own story. From running a fortress to adventuring in the wilderness, it's all about the tales you make in the world. You can view these tales in-game as well, through the Legends mode. It has a rather high barrier to entry thanks to the initially confusing interface, lack of a clear objective, and ASCII graphics, but if you give it time, it can consume your gaming habit. You can download it from the official developer website or through Big Download (Mac and Windows). The Big Download Windows download also includes a sprite pack as well as the game itself.
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