Breakdown of the Arrow season 4 trailer tells us that this show is finally coming together to blend its tv world with its comic book origins. To tell not only Oliver Queen’s story but those around him.
1. Oliver Queen’s Happiness- It looks like that the dark brooding Oliver that we have gotten to know over the past three years is gone. Now with his love for Felicity cemented in domestic bliss, we finally get to see an Oliver closer to his lighter hearted comic book counterpart. As a fan of most things “canon” I have to say that I am in love with Olicity and always will be.
2. Star City- Now the only thing that makes the re-renaming of Starling City back to Star City in honor of Dr. Ray Palmer not as sentimental as it seems is that anyone who is a fan will know that Ray is not dead since he is ‘The Atom’ and Brandon Routh is a member of CW’s Legends of Tomorrow
3. The ‘Justice League’- In Oliver’s absence his family and friends have taken up his mantle with his ex-girlfriend Laurel Lance (Katie Cassidy) and sister Thea (Willa Holland) teaming up to protect the city.
4. The New Suit- After it seems that Laurel asks Ollie to come out of retirement, because as she tells them ‘We need the hero.’ Felicity unveils the new ‘brighter’ Green Arrow suit, reflecting her guys new found brighter outlook on life.
5. Constantine- Matt Ryan is scheduled to appear on Arrow’s fourth season episode Haunted (slated to be episode 5), in a “one time only deal” facilitated by DC that will involve his character being brought in due to his knowledge of Ra’s al Ghul’s Lazurus Pit and the resurrection of Sara Lance (Caity Lotz). "Unlike Thea, who wasn't fully dead [before being resurrected by the Lazarus Pit], the consequences of using the pit on someone as dead as Sara creates some unforeseen difficulties...and John Constantine is uniquely suited to help our team deal with those." Co-showrunner Marc Guggenheim said.
6. Nyssa al Ghul- Speaking of those possibly connected to Sara Lance’s resurrection, the presence of former Heir to the Demon Nyssa al Ghul (Katrina Law) gives fangirls and boys hope that we might get to see a Nyssa/Sara reunion or even more of the burgeoning Laurel/Nyssa friendship we were given last season.
7. Felicity’s sidekick- Comic actor Echo Kellum is joining the Arrow gang as Curtis Holt a.k.a Mr. Terrific of comic book fame. Seemingly joining the team as some sort of assistant to Felicity, its yet to be seen if he will be taking on more of his comic book character's attributes.
8. Damien Darhk- With the season 3 demise of Ra's al Ghul (Matt Nable) his arch-nemesis Damien Darhk (Neal McDonough) has stepped into the shoes of season long baddie (which is sure to yield multiple 'one off' bad guys to keep Oliver and company busy throughout the season, including comic book rogue Anarky).
9. Lance Family Drama- Season three was particularly hard on the Lance family with the (once again) presumed death of Sara Lance and her sister Laurel taking over the family business, (and canon shoes) finally becoming Black Canary. It was also when Laurel thought that her recovering alcoholic father Captain Quentin Lance (Paul Blackthorn) couldn't handle the death of his baby girl again. Turns out that he couldn't and fell off the wagon after he found out. However he also shut his other daughter out of his life, but it seems that those bridges might be on the mend this season.
10. Jeri Ryan- The Star Trek: Voyager alum comes to Arrow as Mayoral candidate Jessica Danforth, a friend of the Queen family. However, seeing the fates of the last two mayoral candidates Moira Queen (Susanna Thompson) and Sebastian Blood (Kevin Alejandro) doesn't give me much hope for Miss Danforth's viability as a long lasting guest star.
11. Lance & Oliver ‘Inspired Monsters’- The dance between lawman and vigilante is one that is fraught with issues on both sides. However if seems that Quentin can see that he is becoming to be outnumbered by the 'masks' in Star City including that of his own daughters. He points out to Oliver that with the arrival of better vigilantes there are going to be better more 'inspired monsters' to contend with.
12. Amanda Waller- The arrival of Miss Waller (Cynthia Addai-Robinson) tells us that unless they are bringing her into the present than we are in store for more Arrow-patented flashbacks to the 'darker' Oliver.
13. Diggle and Oliver Drama- Last season, John Diggle (David Ramsey) lost faith and trust in his best friend Oliver and it showed with their relationship becoming fractured and at the end of the season all but lost. One of the main hearts of this show is this duo's friendship, so it has to be another relationship that's due to repairs.
14. Lazarus Pit Effects on Thea- Last season saw the near death of Thea Queen at the hands of Ra's al Ghul in his attempt to get Oliver to take his place as the Demon's Head. As most fans know, the Lazarus Pit gives life yet it takes from the recipient as well. Taking part of their mind, as witnessed by Thea's memory loss or even by taking part of their soul.
15. Nyssa vs. Malcolm Merlyn- This has been coming since the finale, when Malcolm Merlyn (John Barrowman) took over the position of Ra's from Oliver. Nyssa, still bitter over being passed over by her father as leader has vowed to kill Malcolm to take her rightful place as the head of the League of Assassins. It seems from this scene that something is going down or perhaps just a spirited sparring match between League members.
16. Team coming together- Synchronized jumping and window breaking? Seems like the new Star City quartet has ironed out at least some of their differences to work together to take down some bad guy or another.
17. Sara Lance- Of course one of the best bits of this trailer is the scenes of the resurrection of Sara Lance. Just those few seconds of the formerly dead woman was enough to get anyone ready for 2016's Legend's of Tomorrow. However like Thea, Sara has to have been changed by her time on the other side. She wasn't near death like Thea had been, she had been dead for several days if not weeks or months.
18. Queen vs. Darhk- As usual season 4 is full of one off bad guys and more and a few leeches of the principal antagonist Damian Darhk. The overall arc is going to be getting Oliver back in the fight and defeating this guy and it shows in the trailer. Darhk is going to push Oliver mentally and physically.
19. New ‘Green’ Arrow Logo- Gone is the battered and worn arrow of old, as well as the severe League of Assassin's arrow. Now the arrow is fresh, new looking and (obviously) green just like the bearer.
20. J. R. Bourne- The Teen Wolf alum is playing the villain Double Down who in the trailer is giving Felicity and Curtis some trouble.
*Bonus* Felicity’s badassness- The trailer tells us something that all of has known for years. Felicity Smoak is a badass!