Didn't someone say they did 12 takes of this scene or something (or was that FNIT)?? I'd give a lot to see the other 11 too. 
Anyway, back on topic--I love the way they're barely tasting one another at the beginning of the kiss, but then they let themselves go . . . Jack kisses Ennis's forehead, smoothes back his hair, Ennis clutches Jack, strokes his chest--and finally they drink one another in, lying on top of one another, totally immersed in one another from head to toe.
Mmmm!
And one of the most touching scenes I have ever witnessed. 
I'm loving all these comments about this gorgeous and hot scene.....I was getting hot just reading all your comments!!! And not just cos you were talking about smoking.

But yes, Shieldmaid, you express yourself so well again....better than I could. The first SNIT kiss compared to the next one, when they are lying down, is so gentle, and the way Ennis initially hesitates....to me, its Ennis saying "ok, I want this, I want Jack, but I shouldnt want it, but I cannot stop myself....here goes"......so after that first initial kiss, and they stop to take it in, to take each other in, with the gentle touch of their foreheads together, and Jack's beautiful reassuring words, they lie down, and Jake envelopes Ennis in his arms, and Ennis looks like he has been waiting for this moment all of his life. He clings on to Jack with such intensity, its breathtaking. And Jack just allows him to explore, to touch, because he realises what this means for Ennis, as well as for him.
That second kiss is just something else though.....Ennis is lying back, opening himself up to Jack, ready to receive what Jack wants to give him.
I love that bit right at the end, when they stop kissing for a second, and just look at each other, with their faces still touching......pure beauty and I agree with you shieldmaid, one of the most romantic and beautiful scenes I have ever seen.