I think, on reflection, the dragon-riding sequence is quite a sad scene in an episode that will be viewed through completely different eyes once the show is over. With the Army of the Dead approaching from the north, and with Sam ready to drop the bomb that Jon is a Targaryen, I expect 'Winterfell' will soon be recognised as the last moment we ever got to spend with these characters and simply enjoy their presence. The world is about to come down on top of them all.
There's a post further up this page that accuses the dialogue of being flat, but the action is centred around a line from Varys that captures everything this episode is concerned with in a nutshell: "Respect is how the young keep [the old] at a distance, so we don't remind them of an unpleasant truth: nothing lasts." Whether it's age, the Army of the Dead, or the fact that two star-crossed lovers are about to find out that they're each other's aunt and nephew, something is coming to destroy this temporary peace.
When Jon and Daenerys are out there, kissing and exchanging cringeworthy pillow talk in front of that waterfall, flying through the beautiful vistas in the North, they're having their "A Whole New World" moment. Usually that's the moment in a story where two lovers destined for one another create an unbreakable bond, and Jon being trusted so readily by Rhaegal is a huge deal for Daenerys. For her, it goes beyond Jon simply being good with the kids - he's good with beasts who only trust people they consider to be very special.
And yet, while we're watching them fly through this beautiful scenery and fall deeper and deeper in love, we're aware of a horrible truth that they're still ignorant of. They might survive the attack from the Night King, they might come to accept that Targaryens wed siblings for centuries keep bloodlines pure and that they're doing no different, but their relationship will forever be tainted. Varys' words echo throughout their scenes together. Nothing lasts.
This happiness was always going to be temporary but when it disappears it's going to be gone forever.
