I'm very new to fortress mode, but I've been an adventure mode player for years. I've got to say, I wish I'd tried fortress mode sooner because I've been having a great time with it. Was always just intimidated by the difficulty.
After a couple of forts that got retired before breaching the caverns, (aquifer troubles) I founded a third on an evil glacier for a laugh. Never thought I had any chance at all of surviving there, just wanted to see how long it took before the biome killed my dwarves.
By some miracle things are actually working out ok. Right now we're in our second year, with a walled off section of caverns big enough to supply all the wood and plump helmets we need. Finally got a well set up, a nice dining room and all the other things needed for a basic fortress. Downside is that very few migrants make past all the thralling dust, plus every caravan's ended up being murdered or thralled before reaching the gate. Spent a very, very long time without any water because the first cavern layer was totally dry, had to dig deeper to get a well. That aside though, I've been incredibly lucky. No large-scale fun yet, although I had a ghost problem for a while because of all the dead merchants and caravan guards.
Also this place seems to be very metal poor, even though I specifically looked for a place with both deep and shallow metals. We've got nothing but malachite so far and I've breached 2 cavern layers. :/ By the way, my civ only had steel anvils. Does that happen often or did I just get unlucky there?
Currently I'm planning a weapon of mass destruction to deal with all the thralled yetis and merchants that have forced me to block the gate. I've heard water freezes if it's pumped onto the surface in a glacier, so I can kill people by encasing them in ice. That way I can finally get my hands on those caravan goods lying around outside. (although they'll probably be covered with thrall dust by now, not sure what to do about that)
Adventure mode got me into DF but I can see myself playing a ton of fortress mode over the next few weeks. Loving this game right now. Sorry for the long post.