Like many of the middle episodes, not a lot happened, but a lot was set up. Its a necessity, so while I can't say it was a fantastic episode, it was good for what it had to do.
I'm a big surprised they went from "Dany outside the gates" to "the city has fallen" with just the one scene of Grey Worm sneaking into the city. Since they didn't have Selmy be disguised, it made sense they instead chose him. I haven't read a Storm of Swords in a while, but I don't remember if it happens that fast.