All my personal opinions here
General rule: A+ or higher is overpowered, B- or lower could be improved and i would be happy. Happy medium is B+ to A for all models.
Warcasters:
pSorcha: Overall, she got toned down a bit in MK2. Her Feat is counter-able with enough focus to shake-off effects, though non-warjacks and non-warcasters are still vulnerable. Boundless charge getting cheaper is nice, but Windrush only giving +2 DEF now hurts. Gone from an A 'caster to a B 'caster.
eSorcha: Exciting! I think she has got some interesting new things to play with, and im looking forward to using her. Desperate Pace looks good on any turn Sorcha wont be attacking herself, to get some extra range on those short-ranged guns of the Winterguard. Combined Arms is really cool, seems pointless for using it on massive CRA's as usually you will be hitting on anything but snake-eyes anyway, but doubling up attacks to get RAT7 POW14's with a rerollable to hit is great, especially when you could get up to 6 of them and one RAT8 POW15. With Kovnik Joe helping out with his auto-boost to hit, you will be hitting DEF16 Warlocks and Warcasters eeeeasy. Iron Flesh is cool, im glad shes got it as this on of the better "faction" spells. Cyclone looks like it only hits models that are in range when she finishes her movement, rather than all models in her entire movement? Multifire is cool, good to use on turns your not charging or Desperate Pacing. Gone from a B- caster to a B+/A caster.
pButcher: Hmm. I never disliked Butcher, and always enjoyed Killing Blow. This is gone, and was for a while replaced with Warmonger, which made him AWESOME. This is also now gone, replaced with Full Throttle. Which, i dont actually mind too much. Warmonger was brutal, but made Butcher very ranged oriented. Now hes more melee oriented again. Only '???' thing is Obliteration - really? Why? I think this will very rarely get used. If the enemy is 15" away, and Knocked Down/Stationary, its a good option, but apart from that one situation and trying to get deviations on low ARM troops its not very useful. Also - Full Throttle also gives Butcher boosted attack rolls, which is cool. Gone from a B caster to a B+ caster.
eButcher: Ive rarely used him, usually going with eVlad or eSorcha for 750, but he looks interesting now. His feat still is pretty confusing, but powerful if you get lucky with kills. Ravager and Eliminator dont seem very useful in his spell list, but Fury and Boundless Charge are nice. Although his ability to give free charges to warjacks is better than Boundless Charging them. The rest of his abilities seem the same, homicidal maniac etc. B- caster, hasnt really changed for me.
pVlad: Wow, hes changed quite significantly. Biggest change easily is both S+P and BoK being 4 focus. So you cant cast both in one activation. This is a good change, as it SHOULD stop the unimaginable whining about him. I dont think it will detract from his gameplay very much. When i played him, i usually either went BoK and charged in for some melee using the remaining focus for boosts/extra attacks, or sat him back and S+P while giving focus out to his warjacks OR putting up BoK to give him extra defence. Blood Boon is cool, but not as good since S+P is now 4 focus. Most often i would probably just cast Windwall with my free spell, to add to his protection. (after casting BoK and charging) His feat is good, since jacks can now charge/run for free. (personal anecdote: once i popped his feat and ran with 2 of my zerkers giving them 1 focus each - both blew up when i rolled 1's for both of their unstables :<) Gone from A+ caster to A caster)
eVlad: Well, obviously his feat was nerfed pretty hard from MK1. Mainly no longer boosted attack and damage rolls and an extra attack. Its still brutal though, combined with some of the power solos Khador has. Apart from that, hes almost exactly the same. No different where it counts anyway. Gone from an A++ caster to a A caster)
pIrusk: One cool change i noticed, his feat now gives his troops "Steady", or no Knockdown. This is a nice little bonus! Apart from that, he is functionally pretty much the same. He was always good, and i think they have reinforced that for MK2. B+ caster, no real change.
eIrusk: Pretty much the same thing as pIrusk, a solid caster to begin with, theres one change that ive picked up, losing Full Throttle (obviously he decided to give it to pButcher) and gained a spell called Energizer. Which is 3 focus for +3" movement for all jacks. Pretty situational, probably only going to be used for that one time you REALLY need all the movement you can get. Hes still a 1-2 Jack guy for me. B+ caster, no real change.
Karchev: Well, hes gone quite up and down. Dropped a point of armour, but is able to camp it now which i think is huge, having a ARM25 Karchev with 34 boxes is pretty cool. Fissure is changed to a ranged attack with SP10 (pretty cool, specially since it ignores stealth now) but with RAT5 is pretty hard to hit anything other than a heavy. He loses Iron Curtain, which was a good spell and replaces it with Ground Zero - situational, but one that could be really cool. Would scare off infantry swarms anyway, as it would be instant death to infantry running to engage him. Apart from that, he really plays the same, which is powerful, but vulnerable. Gone from a B- caster to a B caster.
Old Witch: Ahh... well shes taken quite a beating with the nerf bat. Maybe too much. She was all about the control and the tricks, which is very different to Khadors normal strategy. Her feat is way lamer, as before it could stop a lot of assassinations while holding everything in place. Now all the enemy needs to do is walk out of her control range. If they are engaged, just stay still and beat whatever they are engaged with. No combinations will help it out either. Unseen path took a hit as well, since you cant advance after moving. Scrapjack did get reach though, which is cool, he can kill units easier, but the whole feat/UP nerf limits her effectiveness. Gone from an A caster to a B- caster.
Zerkova: Man, she reaaaly wants an arcnode. That would be just awesome. Even something like Vayl's mini arcnode... anyway, she did get better in this edition, mostly with the addition of Razorwind. Which is great, makes her a much better assassin. Twister is cool, it can be cast 4 times and leave 4 3" AOE cloud effects in the field. Problem is, they will be deviating all over the place, and hard to get right. Looks interesting, and i would consider using her now. Gone from a C caster to a B caster. Thats the Warcasters - ill comment on my thoughts about the other Jacks/Units in later posts..
Current Rankings: (according to me)
A: eVlad, pVlad, eSorcha
B+: eIrusk, pIrusk, pButcher
B: Zerkova, Karchev the Terrible, pSorcha
B-: Old Witch, eButcher