The thing about procedurals is that by the end of the episode, nothing really happens. Sure, the perp(s) are arrested, but the nature of the genre is that the characters remain exactly the same at the end of every episode, ready to fight crime as they always have. Writers could certainly do much more with their characters, but for sake of ratings and general ease, most choose not to.
"Countdown" sets up several situations in which more can happen. Castle and Beckett are trapped in the freezer, on the verge of dying and holding each other for warmth. Does anything happen? Nope. They get out alive and, hey, Josh is there. Then, the dirty bomb is about to go off, with the timer ticking to zero. Castle and Beckett hold hands in preparation for the explosion. Does anything happen? Nope. Castle pulls out the wiring and it's all over. And, yeah, Josh is there yet again.
The procedural side of things was very tense, with Fallon nearly going into Jack Bauer mode. There are even two people whose names combined form "Jack Bauer." But the intensity of the episode doesn't completely blot out the useless teases.
After Josh returns and tells Beckett he didn't go to Haiti, she's obviously very happy that he choose her over work. So this thing will drag on longer, with Castle thinking but not doing and Beckett with Josh, but having Castle in the back of her mind.
There are two interesting tweets from Castle creator, Andrew Marlowe. 1) "Dear #Castle shippers. You may be impatient. You may be frustrated. But, trust me, there is a plan." "2) I'm heart, not Hart." Sorry, Andrew, but "Countdown" is exactly what Hart's been up to for six seasons. Hart always says he has a plan, but from we've seen, it's a shitty plan. Having a plan doesn't imply quality. In fact, a plan might me detrimental, depending on how long this is supposed to drag out.
Score: 8.7/10