You have a problem. [SPOILERS.]
And a very serious one at that. It's called sexim. I've watched and enjoyed your show quite a lot now, and wilfully ignoring or excusing the the worst parts of it, but the fridging of Sara Lance is the last straw.
And it is, undoubtedly, a fridging - and a particularly gruesome one. She didn't even get go down fighting like Moira. But Shado, Moira, Sara have all died for one purpose: to intensify the hurt of a man. It's become a pattern. And Sara's death - while shocking, feels meaningless. You will probably say: "But wait, Laurel is the who's suffering most!" Yes, that's how it should be, but you are telling Oliver's story and I'm betting that's where the focus will fall.
And Sara Lance isn't just a female character, she was unapologetically feminist, a protector of others, especially other women, and the only LGBTQ character in your cast (which is otherwise very white and straight).
Sara isn't your only problem: while not killing her, you did the same thing to Felicity this episode: you hurt her just to hurt Oliver. Whatever's happening with Thea? It will surely torture both Oliver and Roy. And Layla and child will surely be held over Dig's head at some point this season.
It's not the first time you've done this, either: whole main plot for season 2 was based on some very problematic stuff - Shado's own fridging being the source of all Slade's revenge. Revenge that took the form of killing more women close to Oliver Queen. (You're also repeating mistakes you made last season: you're bending characters to fit your plot instead of shaping the plot around your characters. Stop it.)
The reason this is so infuriating because you have some pretty well developed female characters otherwise: Felicity, Thea, Moira, hell - even Sara and Laurel. That scene with Laurel and Sara saying "I love you"? I cheered at that. Just like I did at every scene Laurel and Sara shared in the finale. So we know you can do better.
Your show doesn't exist in a vacuum. It is part of an industry that ignores women and where weekly TV shows often fail even the basic Bechdel test even if they do have more than one woman in the cast. Did Sara really have to die so that Laurel could be Black Canary? I'll go for no. Both Sara and Laurel have suffered enough for them to become heroes already, and considering Sara's relative absence, they both could have shared the mask. Or Laurel could have gotten her own alter ego. Perhaps Manhunter? Or even a wholly original one. There's no reason for you to have just one female character wearing a mask, when you've got Oliver and Roy (and Barry) all being superheroes. There aren't enough female heroes on TV these days, and you've just killed one of the best.
It's also an adaptation of a comic book property - a medium filled with problematic storylines for female characters. One by the same company who has a serious problem in its relationship with women. It exists in the context of a culture that devalues women and treats them as objects. In all your interviews you talk about how Arrow has spawned a whole DC TV universe and is in a sense an example. You need to do better.
I was hoping you would be able to overcome the worst problems of the genre you started from and remix comic book canon, but this episode definitely proves you haven't and I'm seriously starting to doubt you can. Due to all this, as much as Felicity Smoak is my favourite TV character right now, as much fun your show is, I'm not sure I can continue watching.