I have spent most of my time so far on Alpha playing Devastation Evoker questing, hitting dummys, and theorycrafting/testing builds. These are my thoughts so far as a player who primarily raids.
I really like the idea of the mastery. It should in theory make Evokers very strong at target swapping, as well as frontload their damage a bit at the beginning of the encounter which can both be great niches in raid.
The ability to stack different amounts of Mastery based on what a raid encounter needs from an Evoker should make the spec pretty flexible in adhering to different damage profiles which I really like.
In Mythic raiding and high Mythic+ content, this class is going to be paper. A baseline 2.5 minute cooldown on Obsidian scales is way too long for the strength of it as a defensive, and needing to commit an extra talent points to bring it down to 90 seconds feels even worse; especially when classes have stronger defensives on a 1m CD baseline (Barkskin). Renewing Blaze is interesting and should help mitigate sustained incoming damage, but won’t help much against burst damage. Zephyr could also be used as a personal defensive, but it would feel bad to have to use something that provides group utility as a personal to stay alive.
In open world/solo content and pvp, the huge amount of mobility should help Evokers stay alive, but in Raids and Mythic+ mobility doesn’t help much when a lot of the scary damage is unavoidable.
There are some passive survivability options in the general evoker tree, like the Stamina increase and Magic Damage taken reduction, but it feels like obsidian scales could use pretty significant buffs for Evoker to have a good defensive toolkit.
I think this ability is awesome thematically and feels great to press on AOE, but on Single Target it ends up feeling like a filler while you are low on resources and not something you want to press as soon as its up. With the damage it currently does to 1 target, there is a chance that on a tough encounter it might end up being better not dealing with the forced movement of it and just forego casting it all together.
One of my main problems with the spec is the clunky feeling I get using Dragonrage. First of all, it is on the GCD. As red spec in AOE, this feels fine because it is launching Pyres that synergize with red talents and do pretty strong AOE burst. Launching out 3 pyres on AoE feels like a good global.
In single target however, especially for a blue focused spec, this feels terrible. This only launches 1 Pyre on single target, which does nothing but a small amount of damage for blue, and the price for that being that the CD is on GCD feels bad.
Another issue I have with Dragonrage is feeling overflooded with resources while using it. Getting a free Essence Burst on every builder is strong, but to me feels very awkward. Channeling Fire Breath and Eternity Surge inside of Dragonrage feels bad because of how long the channels take. I feel like I am wasting time in my cooldowns using them, but the synergy these abilities have with Tyranny makes me want to use them on cooldown as soon as I press Dragonrage for maximum CDR. I don’t know what will end up being optimal mathematically for DPS, but it should feel good to use my 30 second cooldown damage abilities during my major offensive cooldown.
The interesting thing about Dragonrage is that the damage modifier changes based on the targets health, with it giving full effect of mastery on any target through a talent. As a positive, this will give Evokers stronger cooldown windows relative to their consistent damage as the target gets lower, which can have value. As a negative, this makes the CD feel very underwhelming when used on a high HP target, and in raid encounters where things like Bloodlust are used on pull, this is going to feel very bad for Evoker.