O'Brien and Bashir assist a non-Federation world, the T'Lani, in destroying several reams of their terrible and now-unwanted biological weapons, the harvesters. But the two Starfleet officers find themselves on the run once the last harvester is destroyed, when an attacking group of T'Lani attempts to kill anyone with knowledge of the all-too-deadly harvesters.
"Armageddon Game" is a good episode with an action premise that quickly turns into an interesting (if unexpected) character show. The action early in the episode is reasonably executed, and the irony that the T'Lani would need to make sure anyone with knowledge of the harvesters needs to be eliminated—even those who helped destroy such knowledge—is a telling sign of the severity of such weapons.
Meanwhile, the T'Lani provide Sisko with misinformation, claiming the two officers died in an accident and providing a forged video recording of the alleged incident. The resulting scenes on DS9 are hit-and-miss, featuring some absorbing realistic reactions (Sisko's acknowledgement that "the next few days are going to be hard, but we all have jobs to do" and Quark's toast to the deceased "good customers" ring particularly true), and some less effective moments (namely, most of Keiko's scenes, which lack the emotional punch one would expect).
The O'Brien/Bashir interaction is great, redefining the two characters as the most verbally interesting pair on the series—or maybe a close second behind Garak/Bashir. Bashir's backstory comes off particularly believable this time around, supplying the character with a depth beyond what has been explored to date. O'Brien's dialog about family life is also adeptly written. Basically, this show works because it puts two actors in a room, gives them some believable things to say, and the performances deliver. Keiko's investigation that leads her to suspect the forgery is somewhat hokey and a little hard to swallow, but no matter; the surprisingly clever and understated action finale wraps things up nicely.