(My First Siege is a registered trademark of Playfort, Incorporated)
I've been playing since 38c, and this is actually the first time I've been sieged. For my first dozen or so forts, I played with invaders off just to get the hang of resource management and building. Next, I played a dozen or so forts with invaders on, but only got up to three-party ambushes before getting bored with the fort design and abandoning to start fresh. With the new version, I decided to go whole hog, and play until my settlement crumbles or I need to commit regicide.
So, being a fan of passive defense (My walls of tesla coils or bunkers in Red Alert were insane), I decided my fort would only be accessible via a long tunnel filled with traps. I haven't managed to actually fill the tunnel yet, but I'm going for the "death of a thousand cuts" style: single weapon traps, so when the siege goes "Ack! Turn around!" they're already well into the hall of death and need to spring traps on the way out. In the meantime, my initial series of traps consists of half a dozen each of cage and stonefall traps, to be replaced later, followed by 21 weapon traps, all in a 3-wide hallway.
Anyway, it's early summer, and the habitual human caravan arrives. They manage to surprise a pair of kobold thieves in the tunnels, which worries me slightly, but the kobolds seem to just dodge under the wheels of the wagons and get crushed, a point I wished I had combat reports for. Caravan trucks on down to my depot, and I buy the whole thing out with narrow pants. As I'm waiting for them to leave, a vile force of darkness arrives! Yay! Trial by fire for my tunnels!
I watched closely as the group of wrestlers and marksgoblins entered the tunnel, ready to dip down and pull the lever releasing my caged war dogs should they get past the traps. I needn't have worried. Halfway in, they turned and fled, sending two of the surviving crippled wrestlers past a pair of recruits that were loitering on the surface smoking +pig tail cigarettes+ or something.
Anyway, siege broken, and I have another 8 dozen narrow items to stuff in Urist McGee's Closet, the garbage dump above my trade depot.