Pretty good episode.
I liked the Castle Black and Bolton stuff. Dorne stuff wasn't bad, just the weird unexplained appearance of the Sand Snakes in Trystane's cabin.
Dany stuff was good, just because it's something different for her. Mereen was getting stale, but now it should be decent with Varys and Tyrion there to root out the harpies. It's not really clear if Tyrion has command of the second sons and unsullied though. Assuming he does. It would be interesting if word of Tyrion ruling Mereen gets back to Cercei and Jamie.
The Melisandre scene was awesome. A bit disgusting, but eerie and well done with the mirror.
Brienne saving Sansa was good, a bit lucky, but finally a satisfying win for the good guys after a bleak season last year.
I didnt feel sorry for Cercei mourning over Myrcella. In fact I was kind of happy to see her run to the dock like a kid on xmas, knowing she was about to be torn down even more.
Lannisters are in a bit more trouble than they realise I believe. If they send the army to fight the Boltons the Dornish will attack.
If they send the army to fight the Dornish the city will likely be taken over by the High Sparrow.
If they continue to hold the Tyrell heirs prisoner their food supply gets cut off.
Their first priorities should be to aim Ser Robert Strong in the direction of Baelor's sept.