Great fun! And great difficulty! Don't be surprised you will not last a year with your first Fortress as they say. From time to time I start up a Fortress when I have some hours to sink into it. It's good to set small goals for each of your fortresses, I'll admit I never come too far ('Oops that trap system has one tiny flaw, now all my dwarves are dead', 'Oops, water' etc. etc.), but as they say Losing is Fun.
I do very much recommend to grab one of the Tutorials on the Wiki and go through that. They give you enough to do for your first Fortress and are pretty much essential. Also, the
Lazy Newb Pack gives you Dwarf Fortress plus a graphic pack for nicer looks and some other handy tools you may or may not ignore in the beginning. Mostly, I like the graphic pack and the Dwarf Therapist stuff.
Never played Adventure Mode oddly, but thena gain I can keep myself infinitely occupied with Fortress Mode.
