Dwarf Fortress is a CityBuilding/Roguelike game
There are 3 gamemodes in it
Dwarf Fortress:The main gamemode,and the most famous one
Adventure mode:Typical roguelike adventures
Legends Mode:It isn't a gamemode,it's more like a book,where you can go through the history of the world

The game is also well known because it's very complicated
You can make the game easier to understand by installing Graphical Tilesets


Fight Megabeasts and invasions
Create Mega Construction
Test yourself with Challenges

Do anything you want
and remember
Losing is fun!



Links:
Wiki of the game:
Challenges: http://df.magmawiki.com/index.php/DF2010:Challenges
Stupid Dwarf Trick: http://df.magmawiki.com/index.php/DF2010:Stupid_dwarf_trick

I've always considered playing this game, but am not sure where to begin.

Could anyone suggest tilesets, tutorials, etc?

I've always said that the best way is just to fire it up and open your browser on the wiki; you won't be good at it, but you'll learn. That's what I did.

But if you don't like that approach, there's always the Lazy Newb Pack; and I've seen many people recommending Cptnduck's tutorials, so they are likely to be useful. Haven't watched them, myself.

Cool man, I'll check those out. :)