I enjoyed season 5 of Arrow and think that it was a strong season, but it wasn't perfect. The following are what I consider to be flaws in season 5. Not all of them had an effect on my enjoyment, as some just stood out as funny to me.
Felicity getting Oliver to trust new recruits and reveal his identity very early on was very silly, IMO, as he did not know all of them that well, and he was risking them telling people his secret.
Oliver sparing Tobias in "Human Target" when he knew his secret identity, despite killing people again and having killed people early on in season for knowing his identity. This was an inconsistency and only happened because they wanted Prometheus to kill Tobias, to make him look powerful and scary, and to establish him as a threat.
Oliver and his team knowing that Prometheus had access to police lock-up due to his stars being made from his old arrow heads, and not doing anything about it. They never investigated people who had access to police lock-up. That revelation was just abandoned. It was revealed to get fans talking. It doesn't make sense that they wouldn't investigate the police force.
The 100th episode being rushed. Some examples of stuff that was rushed IMO, is Oliver being scared and wanting to stay happy and be with Laurel despite him knowing something funny was going on, and then the next scene he was with Diggle and questioning things again.
Wildog being so strongly against Metas and Aliens and quickly changing his stance after being saved is another. It makes sense that he would change his mind after being saved, but the way everything happened so quickly was silly IMO. If he was that strongly against them, he would take more time before changing his stance.
The fight against all the villains should have been more drawn out and epic. I also think him saying goodbye to Laurel should have been longer. Due to moments being rushed, they were not as potent or as powerful as they should have been.
I felt that the scene where Chase interrogated the criminal in "Vigilante" was not as good as it should have been. When I first saw the scene when watching the episode live, I thought it was badly done. The acting from Segarra was good as always, but it was poor from the actress IMO, especially when she reacted to him punching the mask. I think there should have been a louder noise when he punched the mask, it could have made him come across a bit more scary. I also think they cut to him smiling afterwards a bit too quickly. This was an important scene as it was supposed to show that he was scary and had a dark side. When re-watching the scene, it wasn't as bad as I remembered it, but I still do not think it had the impact it should have had.
Felicity knocking out BS with one punch was very silly.
Them not telling us whether most of criminals Oliver and his team fight are dead or not.
Oliver getting Chases wife to talking him out of everything he was doing was very stupid. Getting her involved was always putting her at serious risk. I get that they wanted to show that Chase being not allowing is loved ones to be weaknesses like Oliver allows his to be was a big thing that separates them, but they should have done it in a way that didn't make Oliver look like an idiot.
Chase being able to dig up footage of Robert Queen killing someone, despite it being gotten ridden ages ago was a bit ridiculous and hard to believe.
The use of Talia. I thought she started off and was used well in her early appearances, in both the past and present, but then she disappeared for too long and things fizzled out with her.
The use of Everlyn, with her betraying Oliver and his team and joining Prometheus. I gave them the benefit of the doubt at first as I thought there would be an explanation, but there wasn't. Her character betraying Oliver for Prometheus does not make sense. She joined Oliver at the start of the season, so that showed that she was willing to be a hero. After finding out about Oliver being a killer and not liking it, leaving his team and becoming an independent hero makes more sense for her character. Joining Prometheus did not IMO.
The finale was fun and very enjoyable, but while not as bad as the 100th episode, was very rushed. Lots of moments were not as powerful as they should have been, and lots of moments suffered, like the Talia/Nyssa fight which was rushed.