Welp, finally finished my first run with one. It's rather fun and flexible, and as it was a completionist run I topped out at somewhere on the other end of 'ridiculous'
I went 4 points into Spirit to grab Strength of Spirits passive, Grabbed all the Knight Enchanter stuff other than Disruption Field which I could never really figure out how to make proper use of. Then specced in a mix between fire and ice. Then grabbed some lightning just for laughs. What I ended up with (and used) was
1 - Frost Step - this is a surprisingly good damage dealer for me, especially against groups. And free. And with Flashpoint you can sometimes chain it nicely. And also movement. Basically, don't leave Skyhold without it. ^^
2 - Winter's Grasp - originally, before they nerfed Spirit Blade from the ridiculousness that it was at first, I wanted something I could detonate. Then I kept it for the convenient freeze and single target damage.
3 - Spirit Blade (w. upgrade) - nuff said
4 - Immolate (w. Wildfire) - I liked it before I picked my spec, it's a detonator. It's an AOE. And since keeping barrier up isn't a problem for the KE, with Chaotic Focus it hits for a considerable amount.
5 - Fade Cloak - again, needs no introductions. Remember that you can still attack/cast spells when cloaked. ^^
6 - Energy Barrage (w. upgrade) - because proc hunting for mastercrafted stuff and Flashpoint was never this easy before ^^. Also very useful if you want to be at a distance for one reason or another (enemy has an elemental vulnerability to your staff, for instance).
7 - Barrier - I like having it here for utility and because if I'm the only mage in the party, it adds a layer of survivability
8 - Resurgence - Focus is nice, but not really critical, and I like the utility of an instant rez/recovery of HP across the party more than I do of massive AOE damage. One focus ability on the bar is enough for me.
Needless to say, I like to play my KE as a skirmisher who can and does get stuck in. Aim for the largest clump of enemies, Immolate, zip through with Frost Step, if you crit do it again because Flashpoint. Spirit Blade lets me worry less about enemy damage resistances, a mix of fire and ice lets me hurt most things from range anyway, and so on. I like to wear a Barrier enhancer ring and one for Immolate, just because. It's a pretty mobile build, and I've tried a more static one with heavier ice focus (up to upgraded Blizzard) but it just didn't work for me and mobility is too big an advantage to discard in favor of staying near frozen enemies/your ice wall.
For passives other than the ones in the KE tree, I've mentioned Flashpoint before. It's just too useful not to have on any mage build, for me. Clean Burn naturally synergizes with it and I like taking it.
I like taking Mana Surge, though it decreases in usefulness as the game progresses and your barrier isn't brought down nearly as often. It's a nice 'oh crap' thing to have, as is Guardian Spirit - on the way to Strength of Spirits, yes, but worth getting even if you don't want to invest into the Spirit tree more. Frost Mastery, because I like using Frost Step a lot rather than Winter's Grasp.
Winter Stillness, I waffle on. It's _nice_ for a varied playstyle, but if you're zipping about you don't use it nearly as much as you would pre-specialization. While it's almost a must for other casters, for KE I'd call it mostly gravy.
Conductive Current - I get more use out of this than I throught I would, when I basically picked it to capitalize on how fighting large enemies with Spirit Blade actually makes your mana go down since there's only one of them. Useful.