Generally, your goal in the Class Tree is to reach the capstones while picking up fight/dungeon-dependent utilities. This means things like extended siglis for longer silences, range on interrupt, purge, stun from Chaos Nova, and the group defensive Darkness. These talents can and should be talented if they suit the content.
The capstones are of varying value. Collective Anguish is pure damage, albeit a significant amount of it. The Hunt is a large cooldown that also grants 50% Leech against your main target of the spell for 30 seconds. Elysian Decree is now a talent on the class tree taking the place of Quickened Sigils. Offering an option with both offensive and defensive power.
Beyond, there are only two talents that are borderline mandatory to take. Rush of Chaos makes Metamorphosis a 2-minute Cooldown rather than a 3-minute cooldown. Demonic grants 7 seconds of Metamorphosis when you cast Fel Devastation. Both of these add significant defensive tools to your kit.
Your goal for Single Target will be to go down the left side of the talent tree and pick Soulcrush and Soul Carver. On the right side of the class-specific talent tree, and then right down to get Fiery Brand and Fel Devastation talents.
The rotation is very simple, you build Fury with Felblade, Fracture and Sigil of Flame. You then spend it on Soul Cleave dealing good damage and stacking up Frailty for damage reduction and Leech.
Demon Spikes and Fel Devastation will help you maintain some mitigation during times when you do not have Fiery Brand up on the boss and your next available Fiery Brand.
The largest change in 10.2 is that with the major Single Target buffs to Soul Cleave you can play without Spirit Bomb in Single Target Raid encounters without any major losses in damage or defensive value.
For Cleave, you basically play the same build as in Single Target. However, you move a talent to Burning Alive to Spread Fiery Brand for damage and defensive value, and talent into Spirit Bomb for extra AoE damage.
This adds significant Cleave damage since Fiery Demise will apply to any target affected by Fiery Brand. In a Cleave or Multi-target scenario, you will replace Soul Cleave as your primary spender and use Spirit Bomb to spend your souls.
This new Mythic+ build centers around maintaining Sigil of Flame on your targets to gain souls from your new 4pc, as well as Parry from Illuminated Sigils. You also have all kinds of improved defensive cooldowns available to you.
Fiery Brand related talents got major buffs. Burning Alive now spreads Fiery Brand to targets twice as fast. Charred Flesh now also always extends the duration of Fiery Brand and now also extends Sigil of Flame.
Fel Devastation and Metamorphosis also got their cooldowns reduced by 33% each, giving you the option to have very high Meta uptimes.