Traps can be OP if you know how to utilize 'em and abuse the pathfinding. Like, enemies tend to A) follow their leader, even if they die, which cause them to gather up around the body(if there's no dwarf or tame animal to draw aggro) and B) they can go down a straight line if there's only a 1-tile wall between corridors(like, enemies following the leader or trying to gather in a mob path around the wall for whatever reason).
Weapon traps can be quite useful in abusing the single-line motion, you don't even have to kill the entire force to have a squad retreat, but there's the problem that weapon traps can get stuck. Leading your dorfs to go and fix the traps. Possibly drawing aggro. Especially when there's a dozen bowgoblins there and your legendary metalcrafter(who JUST finished making a tin artifact) walks up there, gets scared and runs right at the goblins in an order to escape.
Crossbow traps? They require ammo to work, but if you have enough goblinite you can probably supply them with all the metal bolts you'd want. Also, they never get bodies stuck in 'em so they'll keep on firing even in the toughest of sieges, as long as there's ammo that is.
These days when I make traps, it's the unconventional ones. Like right now I got a siegekiller trap. A loooong twisty corridor that I open when there's a bunch of siegers about. They'll path in, a lever is pulled, the whole place is sealed.
Then I pull the lever that opens the watergates. About 2 seconds later, the entire tunnel is flooded. Bye bye siege.
Hilarity occurred earlier though, when a wild animal managed to get in the system somehow and broke the 2 doors that I put up to allow easy cleanup access to the system. The system was still draining. Which it then started to do into the fort. Oh, there were so many people who fell and broke several bones that it wasn't even funny.