It seemed unimaginable that Tom Hanks would appear in a movie with production qualities comparable to those of a SyFy Channel film, yet here is Greyhound – a generally well-paced and uncomplicated story. Director Aaron Schneider and Hanks, who also penned the script, manage to build tension and a feeling of immediacy; for instance, the initial scene where the crew of the Fletcher-class destroyer Greyhound carefully tracks and intercepts a German submarine before ultimately destroying it with depth charges, or when, after becoming the pursued and facing intense enemy fire, the captain of the Greywolf – another, considerably more intimidating, German submarine – contacts the Greyhound to mock the sailors with predictions of disaster. Aside from this disembodied voice, we don’t see any Nazis, and the Greywolf, like Moby Dick, remains unseen until the very conclusion, all contributing to a sense of constant threat. Greyhound is most effective when decisions are being made and commands are issued on the ship's bridge. The excitement of the chase diminishes, however, when we look beyond the vessel and notice that it’s surrounded by a completely digital sea – resembling more an ocean of thick grape jelly. You can criticize Waterworld all you like, but at least it was genuine; I don't mind if they used actual water or simply excavated a large hole and filled it with buckets—the important thing is, it was real H2O. Conversely, Greyhound’s Atlantic Ocean and everything within it – ships, submarines, explosions – feels artificial to an extent that even Hanks’s considerable presence can’t dispel. To me, it felt as though he was simply playing a live-action strategy video game; when characters died, I didn't react emotionally, just telling myself, “it’s alright, they were just background figures.”

Source on TMDB