The biggest obstacle facing the showrunners is to wrap up the central plot and enough of the myriad story threads without seeming like they're rushing it in the final episodes, especially if the pacing suddenly accelerates from the prior pace of the series.
In general I thought they did a decent job with the pacing of this episode and overall I liked it. That said, I take umbrage with two elements from this episode that both reek of Deus ex machina:
1) How did Euron build 1,000 badass ships in the time it took Theon and his sister to sail to Mereen to meet up with Dany? If they could build an entire ship in a day, every day, it would take them 3 years. To make matters worse, the Iron Islands are not exactly covered in good timber. Just sourcing the materials would probably take a year.
2) Sam sure got lucky that one of the first 3 books he selected out of the seemingly thousands of books in the restricted section held exactly the answer he's looking for. It appears he solved the monumental problem with a single all nighter. Kind of reminds me of how I tried to get through college and law school...but I wasn't attempting to save the world.