I've also been reading up a little bit on dwarf fortress, with all the snippets of info cropping up here. So, a few questions for Mr. Fenris here, and any other DF aficionados:
How true is it that each person/dwarf has a personality, and how deep does that really get? And because of this, how much control do you really have over your group?
Yeah, each dwarf does have a personality. They got likes/dislikes and various other aspects like being social or asocial, hardworking or lazy, law-abiding vs criminal tendencies etc. These can affect various things when it comes to the individual dwarf (a hard-working dwarf obviously being somewhat more efficient than a lazy one), but largely affects happiness and friendships. Dwarfs with similar personalities are more likely to become friends.
Personality in the game is also likes and dislikes. All dwarfs prefer certain types of colours, materials, foods and such. When they get those materials they like, they become happy. If they end up in a position of power, they might mandate the construction of more things they like (like my baroness with a real love of gauntlets). When making artifacts/engravings, dwarfs are also more likely to make it depict something they like or dislike, as well as historical events in the game world.
You mostly just control the dwarfs through job designations, yeah. Like, designate those areas to be mined, those trees to be felled, these workshops to be build and different workshops to build different things (eventually its better to just designate jobs 'centrally'). The dwarfs will do the jobs they are set to do (which you can customize, or it depends on their profession which largely depends on their skills).