These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Author's Saving Throw: Iris West is changed from a journalist to a criminal psychologist, likely to avoid Lois Lane comparisons. However in the second episode, we learn she's taking a journalism class for an elective, and she ends up doing articles about the Flash.
We are seeing developments of a shared DC Universe, even if it is in tv form, while the DC Cinematic Universe is lagging behind and studio execs are hesitant on the shared DC Cinematic Universe concept.
This got worse when DC revealed plans for the next several films in the 'verse, revealing that the DCCU Flash is also going to be Barry Allen, rather than any of the others who have worn the suit.
One combined with a stealth pun: In episode 2, Stagg is played by William Sadler, who plays the president in the MCU. Wells killed him. DC killed Marvel!
Fridge Brilliance: Harrison Wells mentions that while Barry was in the hospital, his heart kept speeding up so fast the machines couldn't read it. A little thinking makes you wonder how he knew that Barry wasn't just flatlining. Thus, foreshadowing that he's from the future and already knows that Barry will become the Flash.
"Lightning gave me abs?", from the scene where Barry wakes up from his coma and discovers his powers have made him more physically fit.
"Did Flash run backwards twice?", from the posters showing him running with a lightning bolt shaped speed trail, suggesting he just randomly decided to run backwards twice for some reason.
"Every episode of The Flash should end with Harrison getting up from his wheelchair and doing/revealing something unexpected.", from the episodes were Harrison would stand up from his wheelchair and perform some sort of plot twisting-reveal while smirking menacingly.
Narm Charm: Barry's speech in episode 2 to the STAR Labs gang about how "they all got struck by that lightning" can be a little cringe-worthy to viewers but Grant Gustin sounds earnest enough to make it heartwarming enough to work.
Nightmare Fuel: The Reverse-Flash is depicted as a screeching Humanoid Abomination that's only visibly definable for brief moments; the rest of the time he just looks like living lightning.
Multiplex's M.O. of killing people by surrounding them with his clones and beating them to death.
They Changed It, Now It Sucks: The changes made to the Flash's costume from the comics have received some criticisms - namely the Chest Insignia lacking the white centrepiece; and that the character nicknamed the Scarlet Speedster isn't actually wearing his distinctive scarlet/bright red, but rather a darker maroon or burgundy. However, the final shot in the pilot reveals that in the future the Flash will have a costume that has these alterations.
Uncanny Valley: Some of Multiplex's clones move in a shuffling and unnatural way after he spawns an entire army of them to deal with Barry. It's justified as the more he spawns, the weaker the original becomes and his control over them gets spotty.