I'll have to start off by saying what everyone else wants to say:
Oliver Queen is slacking. Also SPOILERS for anyone who hasn't seen season 3, move no further. I'm about to drop a bomb...that hasn't happened yet...
Well, maybe not, he DID kill Ra's al Ghul and assume his mantle and then hand that title over to his mortal enemy.
Alright, so now Malcolm Merlyn is free to antagonize Bruce Wayne. Hey here's something cool, what if Thea forgives Malcolm for all his bad-dad tendencies and goes to live with him at the League of Assassins fortress place and changes her name to Talia?! Okay I'll shut up. The show is about Arrow.
Since I can tell the future and I know what is going to happen on the NEXT season of Arrow (not really), I'll drop a "what if" spoiler for the post credits sequence for the last episode of the 4th season. Ready? Here we go.
Let's say Thea DID join the League of Assassins under her father. She's already proven to be an effective combatant and even became "Speedy" by the end of season 3. Let's just turn that red hood black and BOOM. Talia al Ghul.
Let's say Talia develops ANOTHER sibling rivalry with Oliver Queen and they start fighting blah blah blah. Skip to the end of Season 4.
Malcolm Merlyn and Arrow are back at it again in an epic battle to the "death" (in quotations since now we have Ra's fountain of youth and no one can really die anymore...) but Talia jumps in and slips a poison dagger into Oliver's side.
Where's The Flash? ATOM? Diggle? Well, probably off on some escapade on the other side of the world trying to help, I dunno, Wonder Woman or something. Oh wait...same side of the world. She's Amazonian. Anyway, they're not here.
Arrow's a badass, we all know that. Somehow he manages to fight off Talia AND Merlyn ALONE. Well...
BOOM. CUT TO BLACK.
Yeah yeah, I'm stealing GIF images from Arkham Origins, shut your face. Let's take a look at the context here, Arrow has just beaten Ra's and Talia AT THE SAME TIME, then Deathstroke shows up to finish off his most hated enemy.
Diggle's asked a favor of HIS most hated enemy to look after Oliver. Deadshot's a mercenary, and a man of honor. He wouldn't hurt Oliver unless he was paid to do it. But, by now we all know where this is going...
Ok...so if Batman is Arrow...who shows up...
None other than Supes himself. And then the episode REALLY goes off. There.