"The Flash" and "Arrow" crossover delivers on its promise of a fun-filled, action-packed extravaganza.

According to Den of Greek, "Legends of Tomorrow" is "an absolute delight from start to finish," which has been able to successfully "blend fan-service moments, gags, character-building and plot."

"The Flash" episode brings the two highly-popular DC characters together anew to establish a "masterful backdoor pilot" and provide a major boost to both CW shows that has now gained a wide following.

"Legends of Tomorrow" focuses on the introduction of arch-villain Vandal Savage, the Hawkman-Hawkgirl reunion, and efforts of the Star Lab team to boost Barry's speed to enable him to confront Zoom.

Although this season of the "The Flash" and "Arrow" crossover highlights the entry of Vandal Savage, the episode gives the two shows "a scale a scale that Arrow especially has struggled with lately."

Among the memorable scenes of the superhero crossover include Cisco criticizing the new Arrow hideout, Barry making fun of Oliver's speech at the party, and Merlyn's dramatic entry into the room.

"It was like a DC TV Christmas party, such was the sense of fun and celebration present in those scenes," Den of Geek said.

But what makes "Legends of Tomorrow" stand out was its ability to show the human side of its main characters, who openly interacted with each "with a full sense of self."

"We know all of these people really well by now, and seeing that come to fruition is the inherent pleasure of a crossover episode," Den of Geek pointed out.

In the meantime, Forbes describes the "The Flash" and "Arrow" crossover as "a much more epic, epoch-spanning adventure of love and death, ageless tyrants and flying...angels?"

"Legends of Tomorrow" renews the strategic collaboration of the Star Labs/Oliver Queen teams who must combine forces to confront the major threat posed by immortal Vandal Savage whose mission is to find Kendra/Hawkgirl.

Forbes likens the episode's plot to the Will Smith Movie "Hancock" that deals with themes of spiritual rebirth and finding one's soul mate, wherein Hawkgirl and Hawkman who must find each other in order to renew their centuries-old romance.

"For four-thousand years she's been killed and reborn, and in each life she's drawn to her soul mate-Hawkman-this time, Carter Hall," Forbes wrote.

The secondary plot of this seaon's "The Flash" and "Arrow" crossover also proved to be interesting, as Dr. Wells and Dr. Wells must combine their brainpower to develop a speed serum which will enable Barry to take on Zoom and save Central City from chaos.