It certainly starts strong with a very distinctive hook. The mysterious cubes raise lots of questions and there's no immediate answers. And then we get some solid character building scenes between Amy and Rory. There's been a running theme this season about the Pond's slow departure from the Doctor's life.
The introduction of Kate Stewart (daughter of Brigadier Lethbridge-Stewart) is another high point early in the episode. Jemma Redgrave plays the role with appropriate authority and it's always nice to see UNIT return.
Then we get some really cool looking and very Moffaty aliens (creepy weird shaped mouths seems to be one of his things) along with the first hint that yes as we had assumed the cubes are up to no good. But then it goes off the rails with some irrelevant side trips that serve to hamfistedly reinforce what we already know and provide some rather goofy comedy moments. It wouldn't be that big a deal except this is a single episode story so time is at a premium.
And that's the pattern for a lot of the episode. We get moments of tension and forward momentum then everything comes to a screeching halt to make it clear to us... again... that the Ponds will be leaving soon. But we already know that. It's so over the top that it has me eager for their departure instead of sad to see it happening.
But all that good stuff gets crammed into a few minutes towards the end of the episode and while it's hardly uncommon for a Doctor Who story to rely on unlikely convenience, in this case (being right next to the hospital that's one of the 7 key transmission points, and Rory's Dad being kidnapped by the aliens) really makes that very obvious.
The Shakri are also quite an interesting concept. The pest controllers of the universe. It's something that deserves exploration it really doesn't get here.
And then there's the cop out ending. Sure it was obvious they weren't going to leave all of those people dead. But really... we just restart their hearts and there's no brain damage or other consequences?
So yeah. Almost a great Doctor Who story. Chris Chibnall came close here and if he'd been able to write an entirely stand alone episode he might well have succeeded. In the end though, I wonder how many elements he was asked to incorporate to fit the larger arc of the season.