Just finished my first fortress. It was 'fun'.
I started in a peaceful and safe place. I was gradually expanding and nothing bad happened for two or so years. Then I discovered a cave system containing a legendary beast. My small, unexperienced militia was sent into the depths to possibly maybe slightly harm this beast. The first one to arrive was the squad leader, my favourite dwarf, named after myself. About three miner dwarves had already been slain and lay about in various states of brokenness. The squad leader charged the beast alone and got completely ravaged but somehow survived. He crawled away into the cave system with massive injuries. Expecting him to bleed to death, I left him and observed the rest of the militia. Unfortunately, by the time I looked for them they were already in pieces. The legendary beast had flown straight up my staircase and had decimated the dining room. However, the beast had suspiciously died and its body was gone.
And thus began the depression spiral.
As many as 20 dwarves were rampaging at a time in a fortress of complete chaos. The sqaud leader, one of two surviving militia members, was in a bed in the hospital. The chief medical dwarf was diagnosing him, oblivious to the crazy goings on outside. Suddenly the other militia member, a wrestler ran into the room and started punching the squad leader as he lay on the bed. The doctor calmy smashed his fist through the brain of the trained warrior and returned to disgnosing his patient. By now I had decided the fortress was doomed and just watched as the dwarves destroyed themselves. Shortly after this, my farmer-dwarf sprinted into the hospital, punched the doctor through the brain, and ran out. Similar chaotic situations unfolded as my few coffins rapidly filled up. Eventually the squad leader somehow got out of bed despite his devastating injuries, hauled himself downstairs to the dining room and slaughtered every single dwarf in sight before finally succuming to his injuries.
Then, at the most convenient time ever, my first goblin ambush. Nice timing jerks. The gate was closed. By now most dwarves had begun to calm down and my population was down from about 80 to 15. My major production is now coffins. Gradually my dwarves begin to grow dehydrated because I had no well. The gate is opened and the goblins killed (with heavy casualties). I abandon my first fortress.