I love the chemistry discussion. I've been trying to think of other films where the protagonists radiate something close to the level of what Jack and Ennis do in their scenes together, but there really aren't that many that spring to mind. Some of the Hollywood classics, perhaps. Neither is it to be seen in the various Heath Ledger/Jake Gyllenhaal movies I've watched by now.
I think that by chance and grace and actor/director dedication, BBM ended up a one shot thing in the chemistry department.
Chemistry cannot be fully defined or explained, but perhaps the fact that it's so obviously there betweeen Jack and Ennis is one small part of the reason why interviewers could *never* stop with their inane questions about the kissing that the acors had to endure in each and every interview.
Now, about powerful film scenes..... I know this is not the kind of scene the thread is asking for, but take the closing scene of A Knight's Tale. The hero has overcome every obstacle and has gotten his girl, and they're kissing in the middle of the arena with all the spectators cheering them and while the camera swoops around them. I don't think it's an especially powerful or unusual scene until I do some fantasy alterations to it: Substituting the jousting arena for a rodeo arena, making the cheering spectators put on cowboy hats, and then substituting Shannyn Sossamon's midieval lady character with a young Jack Twist in his black hat. Now that's a fairy-tale happy ending scene that would have made an impression and that I sure *wouldn't* have minded getting to see just *once*, to offset the devastating impact of the real and perfect BBM.