In Legion I started out feeling sluggish and somewhat meh but after unlocking the various abilities on the AP track I progressively fell into a solid rhythm. Once set bonuses came into play there was a distinct specialized flavor to the class and I felt genuinely powerful.
So far in BfA I started out feeling sluggish and then as I leveled up and lost access to artifacts I felt even more sluggish. I have fallen into a rhythm but it doesn't feel like it flows nearly as well and is far too dependent on spamming Arcane Explosion and Arcane Barrage.
I also preferred having powers that made me shoot more Arcane Missiles versus powers that involve a small dinosaur crawling out of my butt and charging the enemy.
Check this page out. Evocation and Arcane Blast traits are the strongest. One's that do flat damage are behind those two. Rezan's (the little dinosaur) is after those. The Evocation one changes your rotation a little, in that before you go into a second burn stage, you'll really want your Arcane Power and Rune of Power ready to go, so it can stack with the +3250 Int you get from it. If you have multiple Evocation traits, that's up to 9750 Int for 15 seconds. Arcane Blast one is pretty boring, but affects the core of your damage.
AOE is AE+AB spam with Rune of Power/Arcane Power. Basic bitch stuff.
ST is a cluster fuck
1) Charged Up -> Presence of Mind -> Rune of Power -> Arcane Power -> Arcane Blast to 0% mana -> Evocation -> Arcane Blast to 60%
2) then Arcane Barrage, Blast to 4 charges, Barrage, until you have about 8s left on Evocation/Arcane Power
I hadn't played my mage (save like 5 minutes during Cataclysm), since 1.10, where I had a 31/0/20 build, so it's been a long time since I played mage, and holy shit is it so much different. I miss being able to interweave different types of spells - stacking Flame Strike before a Blizzard, or whatever. It's taken a while to get used to the sterilized, and dramatically dumbed down version of the class. At the same time, they've kind of balanced the talents around extra buttons or passive rotating buffs, and between AOE/ST.
I will say the class has felt a lot stronger the higher my ilvl. Below 320 felt like shit, 344 feels very strong. And using the right talents for the situation can really, really help.