My strategy so far has been to -- wait, goblins? What are goblins? *whispers to the dwarven historian*
Oh! Those! They got wiped out about 500 years ago. Elves too, about 278 years ago, although a few elves survive as members of some human civilizations - administrators of some sites even.
We've really only had to fight a couple winged firebreathing handless titans, which were basically buffets with wings. Their fire was apparently so low in temperature that it was unable to harm any of our dwarves. Just the same, the things wouldn't die until the military equipped with steel axes got around to attacking them (Apparently neither "defend fortress" nor "kill [titan]" required actually attacking the titan(s) inside the fortress, but the military was quite happy to kill it if they saw it while deploying to a destination point).
Our biggest actual threat right now is a former mayor who has lost his grip on reality, and believes that he did not lose the election. In addition to demanding that he retain his bedroom and office (yeah, right), he went completely mad and mandated the construction of slade items! We threatened him with drowning (by putting him in a drowning chamber and slowly filling it with buckets), but he relented on the mandate (when the water reached 3/7), only to pronounce a sentence of jail time for an armorsmith upon being released from the chamber! I do believe we're going to have to exile him to a mental hospital, which is under construction as we speak! (It's really quite hilarious, except for being annoying that I can't simply have him executed without screwing the game all up.)
We have yet to dig very far underground, however, but have prepared a trick for when we do. We'll be collapsing an entire hall and all the levels below it, which have been dug out as well, directly into the caverns below (once we find them), bringing a lot of rock raining down on the monsters' heads and turning our tunnel leading to the underground into a massive pit at the same time. Then we'll build supports one level down from the hall, and on the hall level, scattered floors to support covering the entire hall with hatches. Then we'll link the hatches in a checkerboard pattern to each output of a two-output repeater, and Urist's your uncle: Anyone trying to walk down the hall while the repeater is turned on will fall all the way to the cavern floor and go splat. I've built this before, and it consumed entire goblin sieges as they charged across it. (It just remains to be seen if everything is susceptable to shattering into their component parts in this version, and just how expansive the underground caverns really are; I'm only guessing at this point. Plus the military will have to hold off any invasions while things get linked up, which could take a while, especially if anyone down there can fly.)
Summary of the last paragraph: Who says traps are useless? The problem with your traps is that they aren't megatraps.