Enter Zoom as the title of Episode 6 of Season 2 of Flash suggests, is the introduction of Zoom (voiced by Tony Todd) with more depth into his motivations and the extent of his abilities, which revolve around Barry's self created speed-force.
Viewers of Episode 5 would know the mysterious arrival of Earth two Harrison Well's who is referred to as Harry, much to the dismay and skepticism of Barry's team, who still keeps the same genius that Thawne kept.
'Enter the Zoom' deals with Barry's strive and motivation to end Zoom and stop the breaches to keep Central City safe from Earth two doppelgängers, as Zoom uses people Barry knows against him in order to defeat him. In the wake of the new villain we are introduced to Dr. Light a.k.a Earth two Linda Park (terrifically played by Malese Jow)
Dr. Light in Earth two has control over photokinesis, the episode explores her powers where she can figuratively control light, meaning she has the ability to project energy and also turn invisible (through reflecting). A version of her is kept as bait (don't won't to spoil anything) in order to bait Zoom.
The episode also introduces Patty and Barry as a couple, and I have to say the chemistry between Grant Gustin and Shantel VanSanten is incredible and even more believable than the one with Iris West, who still in my opinion is portrayed dreadfully by Candice Patton. The episode explores Patty and Barry's relationship, and is very understandable as Patty views the world in the same way as Barry, having lost a paternal figure and dealing with the unknown that makes them each as a character stronger as they deal with their road of tragedies.
The main focus of the episode is on Barry's arch nemesis and reverse flash of Earth 2, Professor Zoom, or as Zoom in the show. Zoom's entrance is terrifying and establishes his presence and power immediately when the team faces him, he has the potential to be even more menacing than the reverse flash of season one.
Zoom's primary goal is to be the only speedster alive, unlike Eobard Thawne who wanted Barry to only suffer (thus killing his mother and framing his father).
Zoom brings a whole new menacing spark into a tv verse where the villains are generic (Arrow & Agents of Shield). Zoom is quite frankly terrifying and I cannot tell you enough as the the audience to watch this episode to discover for yourself. Since this is the best episode yet and it looks like Season two of flash is quickening up towards a very exhilarating finale that exposes the viewers to a whole new multiverse that have a major impact on DC CW heroes (A slight cameo of green arrow of Earth 2 of sorts if you listen carefully enough).