Chase's plan has become increasingly muddled ever since he was outed publicly as Prometheus. Up to that point, he had orchestrated the public "fall" of the Green Arrow by forcing him to take the rap for Officer Malone's death. He was also in a position, as Diggle's attourney, to actually keep him behind bars and thus separate him from Oliver. (why he got him out still baffles me...would have far better suited his purposes to make it APPEAR he was trying to help, but in actuality, screw Diggle even more)
But from the moment his identity became public, I've been left scratching my head at his endgame. OK, so he successfully kidnaps Oliver and gets him to admit he enjoyed killing people. Then he lets him go.
Then he feigns (?) his surrender to Oliver because his father was going to disown him. And he says he wants Oliver to kill him - is that his end game now? Forcing Oliver into killing him to prove that Oliver is the killer that Chase believes him to be?
And now he's kidnapped all of Oliver's friends and family, has brought most of them to Lian Yu, and seems to be goading him into a final confrontation. Again, to what end? Forcing Oliver to kill him?
Truthfully, I don't quite get the moral quandary Oliver seems to be putting himself through with Chase. There's a big difference between killing drug runners and corrupt politicians rather than letting them face justice, and letting a psychotic serial murderer run roughshod over your city and everyone you care about. I think Oliver should be able to put an arrow directly between Chase's eyes and be able to sleep like a damn baby.
But, all of that's details...looks like we're in for a hell of a showdown in the finale, and this is the kind of stuff I look forward to as a comic book fan. Big, epic fight with all sorts of notable characters involved. Oliver certainly looks to be aligning himself with some dodgy characters with questionable motivations for helping him (Slade, who arguably hated Oliver more than anyone else we've seen on the show, agrees to help him? Hm.)
Not that I'm not going to enjoy watching them team up. It's going to be badass. But I feel like there's going to be another shoe to drop here, and that Oliver may pay for putting his trust in the wrong people.
One more thing; I see some complaints about "Ollicity" rearing its head again. To me, the issue with that pairing was never about the characters - they had oodles and poodles of touching scenes and great chemistry when Arrow was at its best. But the way the relationship and the two characters themselves were written at the time that they were a couple was absolutely dreadful.
Oliver and Felicity could work as a pair - and indeed, I think both characters are at narrative strong points right now - so as long as they don't compromise who they've become to make them a relationship (eg - turning Felicity from the wise cracking but determined tech goddess into a weepy, judgmental damsel in distress), I think it can work. But we'll see.
EDIT: Stray thought - Evelyn Sharp is also a massive hypocrite of a character. Her turning on Oliver was believable after discovering he was the Hood. But all of her actions since then have defied explanation, as Chase is just as much if not moreso of a prolific murderer than Oliver ever was. Her standing by while innocents are killed and children (William) are put in harm's way don't jive with anything we knew about her. Lazy writing, IMO.