J.J. Watt has apparently turned into a music critic in retirement ... and Taylor Swift has passed his first assignment -- with the ex-NFL star absolutely raving over her following her shows in AZ over the weekend.
The former Cardinals pass rusher hit Saturday's "The Eras Tour" concert at State Farm Stadium in Phoenix with his wife and friends ... and in a full breakdown of Swift's performance the next day, he said he was blown away by what he saw.
In a 2:38 review that Watt posted on his social media pages, he gushed over Swift .