Ok but seriously now.
Shadow Dance: I think this should be the gold standard for CDs. It requires thought regarding when it should be used, offers a noticeable change in the rotation in the form of more CP and bigger numbers, and, for PvP, offers high skill-cap utility. Getting the most out of ShD requires timing and skill in a way that other CDs do not. That isn't to say it doesn't have issues, but most of the ones I've heard are with subtlety as a whole.
Adrenaline Rush: This is a good CD. It doesn't change the rotation in the way that ShD does, but I like the minigame of having to not cap my energy. There is one thing though...+20% attack speed? Nobody cares about it. If you removed that part of Ancitipation and buffed, say Sinister Strike to compensate, I doubt anyone would mind. Sure, attack speed is mad good as Combat, but it is *so* uninteresting. Still the energy portion is enough to make this one of my favorite CDs to pop.
Killing Spree: This is pretty close to Adrenaline Rush in terms of fun. Actually, it is way way way funner than AR in a PvP setting if I successfully use it against just one target. If I end up getting two targets in PvP I hate it. Lots. Like, it gets me pretty annoyed. Inconsistency in a major CD is a good reason not to play a spec in PvP. PvE you can generally remove that inconsistency, and I like the pause and what not. Would be nice if it was better to save it for Max Insight though.
Shadow Blades: It's...ok. As some of my fellow posters said it feels *very* out of place in Subtlety. We gotta deal with ShD and Vanish, both on pretty short CDs, and not overlap them with SB - a feat which requires waiting over a min to use the first ShB if you have the 4-pc, thus being maybe not optimal for the first use? For Combat and Assassination, you just bind it to your other major CD, and/or use it on cooldown, which is...ok, I guess, but not ideal.
"But Hail," you might say, "You first complained you couldn't overlap it with CDs, and then you said overlapping isn't ideal! WTF do you want?" To that I say, "Good question! CDs should make playing more interesting for their duration, and having that increased interestingness spread out more is better than clustering it (Consider SB during ShD - Ambush already generates 2x more CP than BS, one extra isn't that cool in comparison when it could be later). The problem I mentioned with Sub is specific to the spec. Sub rogues have ShD giving 18 secs of FW per min, and Vanish giving 13 every 2 mins. That means 40% of the fight you can't use another CD without reducing the benefit of FW and losing DPS. The fact that you start out the fight with all CDs up only exacerbates this problem. If FW lasted only 5 secs, this would not be an issue, and sub would be the best spec for SB.
"But wait, there's more. You see, there's another better way for SB to have synergy with sub: Make it an interesting cooldown. The autoattack portion if stupid. Nobody notices autoattack damage. 100% armor penetration is a great an significant damage increase, but it is wasted on autoattacks. SB's autattack component should straight up be removed. Replace it with something active. If I have to combine SB with ShD, then so be it. I'll be happy I am not keeping it on CD for a long time.
Vendetta is stupid and useless and dumb.