I have been following Arrow since the start and after a few rocky episodes, the show started to pick up, but there was stil something missing. We would get characters and villains, but their powers would be stripped and they wouldn't often use their names. As the series has grown more confidence, it has allowed itself to be closer to the comics and add in costumes, real villain names and powers.
Arrow is also becoming a huge Easter egg hunt, with what seems like every name used in the show being some character from the comics or at least someone who has worked in the industry. With these small nods we are also able to peak into the DC universe without delving too deep into specific events and characters.
-Minor Characters-
These are characters I'd like to see in some form, but only one to two episodes.
Glorious Godfrey
It seems odd to feature a character who mostly deals with gods in a show that has yet to see concepts even close to gods. But Godfrey is unique, he is one of Darksied's minions, but he is an earth based fella. I'd like to see Godfrey as some political talk show host, who is always berating Arrow and any other "vigilante." It would be a nice thing to see on TV in the background much like the particle collider which was mentioned very often in the first half of this season. It would also be able to create a door, if they ever wanted to explore New Gods or the Fourth World as a concept.
Onomatopoeia
One of Green Arrow's few notable enemies, Onomatopoeia is a great one off villain to use. A simple serial killer perhaps who uses sound to get the best of Oliver, or perhaps he is hunting the Arrow down. You could do a lot with this guy and get away with most of it. He'd be a nice costumed enemy who could perhaps find away to get under Ollie's skin and perhaps comeback to further haunt him.
Prometheus
The cop killer. Usually a batman rogue, Prometheus could be used as a highly publicized killer moving across America killing dirty cops, and makes a stop in Starling City. He could start targeting dirty cops who Ollie was looking into, perhaps Arrow is too busy and turns a blind eye, "taking all the help he can get". But when Prometheus mistakenly targets Quentin Lance, Oliver is forced to get involved and put a stop to Prometheus's terror.
Doom Patrol
Do you guys remember that amazing episode of Smallville, one worth watching even if you aren't a fan of the show, "Absolute Justice." Personally, it's my favorite episode of Smallville, and I think the same effect could be made with a Doom Patrol episode. It could introduce a group of Heroes that the public adores as opposed to himself, who is still in murky waters when it comes to public relations.
-Recurring Characters-
Characters, I'd like to see more than once, but not every episode, but every once in a while they show up to either lend Arrow a hand, or stir up trouble.
Captain Boomerang II (Owen Mercer)
I know, the Flash is getting his own show, it would be somewhat rotten to steal one of his biggest villains. But I feel Capt Boomerang works far better against Green Arrow, seeing as they both use outdated projectiles and are lethal with them. Owen being an anti hero could fulfill a role similar to Huntress, but less crazy. Maybe Oliver runs into this guy, who is trying to make up for the sins of his father, much like Ollie was before, who also fights crime. They become fast friends, but they have a falling out when they don't agree on how criminals should be taken care of, they have a falling, and Owen leaves Starling City, but still on good terms. Leaving room for future team ups.
The Ray (Ray Terrill)
I feel like Ray is a character who is too cool to not get any recognition.
Being a superhuman, it may be harder to pull off, but I feel like he would be good fit, especially if they introduce one of Green Arrow's biggest villains, Dr Light. The contrast between these two characters power sets could make it easy to give them both origins in the same episode, with Arthur Light becoming Malicious and Ray Terrill making it his responsibility to stop his evil counterpart. Perhaps after a couple of episodes of Ray and Ollie tracking Dr Light, Ray is murdered and Dr Light is cemented as one of the bigger villains of the show.
Eclipso
Another possibly odd choice given his connection to the supernatural, but I think that makes him all the more interesting. He could easily become one of the more memorable villains of the show, and even give room for a possible Spectre spinoff. He would be one of the unstoppable enemies, and Arrow has to convince the Spectre to let him handle Eclipso fearing the amount of people that could caught in the crossfire, fights would fights of endurance and willpower rather than just strength and speed.
-Supporting Characters-
characters who would return on an episode to episode basis, for entire seasons at a time.
Azrael and the Order of Saint Dumas
Another traditional batman rogue, but I feel he word fit right into Arrow.
I feel like the Order of Saint Dumas could be an entire subplot for a season, much akin to how HIVE is currently being alluded to. Azrael would make a great antagonist, and the Order itself would be a great place to draw tough thugs from. It would be like using the league of shadows, but less likely to royally screw something up. It could also provide a huge twist at the end, that Azrael was brainwashed the entire time, and the real leader of the order escaped away.
Maxwell Lord
Talk about perfect for this show. Maxwell is an evil business man, practically every episode of the first season focused on an evil business man. So he is right in the vein of the show. Along with these shadowy organizations being introduced left and right, Maxwell would makes for a magnificent reveal as to who has been behind numerous evil plans. It wouldn't surprise me at all if he were behind HIVE or ARGUS. Along with a story where brainwashes Oliver, and someone like Roy or one of Oliver's team mates is forced to kill Lord in order to break the control, much akin to how Wonder Woman killed him in the comics.
Dr. Light
When I say I want see Dr. Light, I mean I need to see Dr Light. One Green Arrow's biggest villains, and you can tell he is being saved for later. I am guessing after all this business with Slade and Blood is concluded, a light could emerge from the shadows and make himself the big bad of the show. Being one of the most sinister villains from the comics there is so much material to pull from. Specifically Identity Crisis, which featured plenty of really great DeathStroke/Green Arrow? Dr Light moments and plots, making it easy to incorporate all three of them while having source material to follow.