It’s normally a tradition of mine to do a “what you need to know” post and a “gear list” post for each major patch that comes out…but real life is still kicking my ass, so you get this abbreviated list of mostly links to better resources.
For a general list of things that’ve changed, my 5.4 changes posts on WoW Insider from a couple months ago are still relevant. (part 1, part 2)
- DoC vs. HOTW vs NV: After spending most of the PTR being inferior to HOTW, a late buff pushed DoC back on top and NV into spitting distance of HOTW. Same guidance from 5.2 applies – Take DoC if you can manage the additional rotational complexity (either via player skill or an easy fight), take HOTW if you don’t want to risk the DoC rotation or you have a use for the HOTW cooldown. I personally run HOTW. Nature’s Vigil is now decent if you use it on cooldown. More discussion here.
- SotF vs Inc vs FoN: Incarnation still sucks (and it actually is worse now than it was in 5.2). FoN and SotF are now roughly comparable – FoN pulls ahead slightly (2-3%) if you have Rune of Reorigination and drop all the treants during a Rune proc. More testing is needed to see if it’s superior for all gear configurations.
- Nature’s Swiftness is gone and is replaced with a passive slow HoT, Ysera’s Gift. The optimal choice will be based on encounter. For steady incoming damage, use YG; for frequent bursts of damage, use CW; for infrequent heavy bursts, use Renewal.
- Trinkets: VERY complicated topic, but a rough stab at an order would be Rune, Ticking Ebon Detonator, Haromm’s, Assurance of Consequence, H Renataki’s, H Juju, Thok’s, Discipline of Xuen. Raffy has a list of pairs here, which is a better way to sort these things. Catus has also been updated to v15 with 5.4 support. Really, you need to do a trinket priority list for each encounter – I suspect AoC will be more broadly useful than Haromm’s even if Haromm’s is slightly better in the sims.
- Also from that thread, Raffy’s rough guess at a BiS list is below. There’s lots more gear discussion in this thread. Enjoy!
Head:  Headpiece of the Shattered Vale
Neck:  Immerseus' Crystalline Eye
Shoulder:  Spaulders of the Shattered Vale
Back:  Fen-Yu, Fury of Xuen
Chest:  Raiment of the Shattered Vale
Wrist:  Bomber's Blackened Wristwatch
Hands:  Grips of the Shattered Vale
Waist:  Cord of Black Dreams
Legs:  Riou's Vigilant Leggings
Feet:  Pandaren Roofsprinters
Finger 1:  Kil'ruk's Band of Ascendancy
Finger 2:  Ring of Restless Energy
Trinket 1:  Rune of Re-Origination
Trinket 2:  Haromm's Talisman
Main Hand:  Hellscream's Pig Sticker