Disclaimer: I posted this on the WoW forums a while ago, but I thought it would be a good idea to gather opinions from here as well.
The following is coming from a pure PvE perspective.
In Legion, the Rogue specs have received many thematic and visual changes in order to portray truly unique themes. This is a change that many of us have been requesting and anticipating for a while, and I am glad to see that it has finally been brought to fruition... However, while I welcome the visual and aesthetic changes with open arms, I can’t say the same for the gameplay changes that came with it.
Heavy mechanical changes were made in an attempt to compliment the specs' newly proposed fantasy… While I consider some to be good changes, some of it is just a downright frustration, and have honestly crippled the enjoyment I once had with this class.
Assassination
As dictated by its revised fantasy, Assassination’s playstyle now has a significant focus on single target uptime. Before Legion, Assassination was highly regarded as the “melee dot spec”, or "melee affliction" by many, which excelled on 2-3 target encounters. What was especially fun was knowing that the more targets you have Ruptured (w/ Poison) the faster your rotation would become. While this is still possible and somewhat relevant today, there are many new mechanics that de-emphasize this as target switching can incur a significant DPS loss.
Before Legion, the major ability that would encourage sticking to one target was Vendetta, now we have the additions Surge of Toxins, Toxic Blade, and Kingsbane. While these add some much needed complexity to the single target rotation, it greatly discourages target switching within these windows. This is especially apparent when you consider how short Kingsbane and Vendetta’s cooldowns can be thanks to Artifact Traits and Relics.
I miss the amount of freedom Assassination had in multi-target encounters and I wish this could be reinvigorated in the future. I don't think it's right to declare Assassination as a single target focused spec because its name suggests that kind of playstyle.
Subtlety
Subtlety’s current state is an improvement over the 7.0 edition, and in general I am happy with the direction the spec is taking. Although, there are a couple of areas that I believe could use some revision.
Subtlety right now is arguably more complex than it needs to be, and resource management is honestly in shambles. Energy capping and combo-point overflow is at an all time high, and attempting to achieve optimal resource management is currently a nightmare. Despite this, I am still capable of doing a reasonable amount of damage even though I am energy or combo point capped 40% of the time, this simply does not feel right.
At the moment, I actually consider Subtlety to have not 2 but 3 main resources thanks to Shadow Dance’s charges and cooldown reduction system. In fact, I see many people using Weak Auras to create a Shadow Dance tracker in the form of a progress bar, which is generally located alongside their Combo Point and Energy trackers. I’m happy to see complexity opposed to simplicity, but when you consider the many different mechanics and resources that need to be monitored with Subtlety, I think it's a bit be too excessive.
In my opinion, Subtlety compliments its fantasy way better than the other 2 specs, and I have very little complaints in this regard. Although, I think its philosophy as a "patient ninja" may be selling the spec short from a greater potential. I would label Assassination to be the "patient elaborate planner", why must Subtlety have this concept as well? If Subtlety had a more aggressive but calculated playstyle, I honestly think it could do wonders.
Outlaw
As for Outlaw… this one probably frustrates me the most. With all things considered, Combat was considered to be one of the most consistent specs in the game pre-Legion. In Legion however, Outlaw turned out to be one of the most inconsistent specs in the game, which is absolutely astonishing. Roll the Bones, in my opinion, has no place in a game like this... I'm happy we no longer have Bandit's Guile, but Roll the Bones is not an improvement... at the very least in its current iteration.
The pirate theme is arguably very similar to the spec's preceding theme. I don't understand why such drastic changes had to be made in order to live up to its "new" fantasy. In all honesty, if only minor mechanical changes were made in the "transition" from Combat to Outlaw, it would be just as believable.
Conclusion
I believe drastic gameplay changes should not have been molded onto the major aesthetic changes. Aesthetics should have been molded onto the existing, time-developed gameplay mechanics and playstyles, with minor changes/additions being welcome.
Thank you to anyone who took the time to read this, and I look forward to reading any opinions / thoughts if any.
Thanks.