It was alright, but it veered too far into the realms of absurdity. I can accept some amount of physics nonsense for the sake of entertainment but this was the episode that went a bit too far. The suspension of belief disappeared to an extent. I can accept things like time travel, sound in space, blah blah blah etc. but:
1) Firstly, any fellow biologists wondering how the heck those moon spiders could possibly be unicellular prokaryotic organisms? It could have been forgiven if the Doctor hadn't specifically said that only scientists would understand. Scientists would know it isn't even possible for highly differentiated, badger-sized prokaryotes like that to exist!
2) Tides would still occur but would be tied to the Sun instead, meaning they would be smaller and with a different pattern, but would still occur - unlike what Clara claimed. I guess that could just be Clara's lack of scientific understanding, but I get the feeling the writer wasn't aware of this fact either.
3) Tides big enough to destroy cities, eh? And yet they travel to a remarkably pristine beach at the end of the ep...
4) The moon creature laid an egg the same size as itself? Huh?