Let me start off by saying Arrow is a great show. It has action, a deep plot, mystery, great characters, etc. But some seasons are better in one aspect than another. For example, the first season had mystery and a great plot. The action sequences were good but not great. Same goes for the characters and their development (Tommy, anyone?). Season 2 brought us great action sequences and a decent plot, but a lot of the mystery was gone and the flashbacks sucked. And now, season 3 brings us awesome villains, a good plot, mystery, and okay flashbacks. But how does one top that? You'd need to mix all the other seasons together.
[Arrow](series:720988) has had its fair share of mystery. What does Moira want? What's the Undertaking? The League of Assassins? Who killed Sara? What the hell is up with ARGUS? Majority of these questions stem from season one or three, the strongest seasons plot wise (in my not so professional opinion). Writers, if you want a good plotline for season 4, you need to remember what you did for the first season.
Arrow has cool action sequences, whether our combatants are male, female, or basically genderless serum enhanced freaks. There is no doubt that season 2 had the best fight scenes. Want to have good finales and battles? Season 2.
I guess this is a general one, but all seasons were good with slowly molding their characters into the next phase of their lives. Don't rush it, but keep doing it.
This part worries me a bit. The first season we had a normal person as our villain. That was pretty cool. Malcolm Merlyn, equal to Oliver Queen. Who will win? The second season topped that, bringing in Oliver's serum enhanced "friend" from the island. The third season will top that yet again with Ra's al Ghul and his League of Assassins. But where do you go from here? How do you top an immortal man who basically has the population of a small country at his beck and call, not to mention these people are all master assassins. You go back to what you started with. Malcolm Merlyn is still alive, and has trained Thea. Slade Wilson is alive. Pair those three up (I strongly believe Ra's al Ghul will be killed by Nyssa at the end of season 3 so I'm not grouping him here) and give Oliver the ultimate enemy. I imagine this would play out with Malcolm (who was working to get Slade off the island) being killed (really killed) in the midseason finale. Thea picks up where he left off after somehow learning Oliver is the Arrow when the show returns. Angered at this revelation, she takes up her father's work and continues to attempt to get Slade out. He gets out, and they work together to kill Oliver. In the finale, Thea feels bad and attempts to back out of this, leading to the final battle, where Thea kills Slade for what he's put Oliver through on the island. This leaves Thea in a mentally ill state for season 5 (which could see her being put in the Suicide Squad). It would give a new story arc for future seasons. Also, I hope Diggle dies.