After getting a chance to play not one, but both specs through full clears of Uldir, I'm pretty happy to say that they both play very well.

Bragging about my own ranks aside, most already know that Arms is outperforming Fury right now, in part due to general tuning and in part due to having a generally better toolkit. That said, Fury isn't as bad as it looks on the WarcraftLogs performance statistics - there just aren't nearly as many people playing it, with 2.3k Fury v 8.8k Arms Heroic parses and 30.4k Fury v 56.8k Arms Normal parses. When most of the better geared players are all playing the same spec (as is expected in a new tier), the other one always looks worse as a result.

Critiquing both specs real quick:

Arms feels really good, especially at higher gear levels.

• I was initially dismissive of Skullsplitter, but it has grown on me over the last few weeks - the ability to generate on demand rage is a much bigger advantage than the tooltip would imply.
• Sweeping Strikes is inordinately useful due to the number of encounters with close range, short-lived adds, which is more alike to Tomb of Sargeras than Antorus.
• Warbreaker + Bladestorm is unparalleled for raw burst and on a short enough cooldown that it's nearly always available when you want it.
• To cap it off, Massacre works very well on a number of bosses who have vulnerability or burn phases near the end of the encounter (Taloc, MOTHER, Fetid, Zek'voz, Zul).

By contrast, Fury feels good, but can't hide its shortcomings. The general rotation is still just as much fun to play as it was in pre-patch Antorus, but some issues stand out.

• Fury simply doesn't have the tools to compete with Arms; its sustained multitarget through Whirlwind is theoretically strong, but no real practical situation for it - any time you have that many adds, they're burst down. Speaking of burst, Fury's Bladestorm is fairly commensurate to Arms', but missing Warbreaker/Avatar/Deep Wounds which push Arms over the top. Couple that with the generally long cooldown, and Fury feels like it's frequently struggling to build the momentum that Arms has every time Colossus Smash/Warbreaker come back off cooldown.
• Siegebreaker reminds me of MoP Colossus Smash (which I loved), but when I play it, I realize the rotation has changed so much that it just doesn't work anymore. The preparation, timing, and strict cooldown were fine in a spec which was designed around it, but now only stifle an otherwise fluid and reactive rotation, so although I want to like it, it's a bit of a let down for me.
• Carnage is so strong, it completely outweighs Massacre, even with those fights that it should be good for. It's just disappointing really.

I expect tuning to hit sometime between tomorrow (Friday) and Monday, so it's hard to say what will happen when Mythic opens next week. I kind of expect Arms to see some nerfs, but it's not nearly as egregious as some other specs at the moment, so I have no idea what will really happen. Rest assured, as soon as there are changes, I'll get to work on analyzing them and updating guides for you all.

Until then, I hope everyone is having a good time in Uldir, and BfA so far in general. It's not a perfect expansion by a long shot, and may be plagued by bugs, but I've found it to be enjoyable overall… though it could just be the fresh content keeping me preoccupied! As a reminder, all of my Arms and Fury guides on Icy-Veins and Wowhead were updated for Uldir release, with new Azerite rankings, BiS, Rotations, Talents, and entirely new Mythic+ and Raid tips pages with talent and strategic recommendations which I'll also be updating as the Season/Tier progresses, so check those out and let me know how well it matches up with your experiences so far.