Uh-oh! This is not a good sign! In fact, this is a really,
really bad sign
Yes, embargos are "normal". But usually they get lifted a week before the airdate, to generate buzz right before people can watch it.
Withholding reviews until the airdate is... unusual. To say the least. And usually only happens when the creators aren't content with a work. Aka they know finished the product, saw the product, and knew people,
regular people, won't know what to do with it.
Don't get fooled: This is not to avoid fan-backlash. This is to avoid
regular opinions. That means problems with the
basics, aka "characters", or "plot". This is so people aren't able to see the horrible
Rotten Tomatoes-score before it airs.
This is the Fant4stic/BvS-way of handling bad reviews