It's early days with the new update, so I'm still playing through battles, challenges, GW, and arena to experience all the changes. A few items I've seen so far:
I don't see the need for protection. Mechanically, it's a just a pile of hit points that attackers have to get through before actually causing damage. OK - I like the idea of a "force field." But as-is, protection plays as a ham-fisted and arbitrary way to handle the "problem" of fast attackers wiping out Toons before they had a chance to strike back. Why not just increase health, improve armour, or decrease damage and have done with it? At the very least, if it's going to be a permanent thing, it should kick-in straight away (i.e., not wait to Gear VII) and there should be a way to replenish it. Otherwise, it's just more hit points.
Advantage now seems broken to me (and I thought it was fine before). All it is now is a way to guarantee a critical hit on the next attack (yawn). Since the Advantage buff disappears after the next attack, the update breaks First Order squad synergy. It also seems to unbalance Toons who use AoE attacks with advantage - an IG-88 or HK-47 with advantage is now guaranteed 1 critical hit against every target (which has ripple effects with HK-47 as a squad leading other droids). Finally, this depreciates the value of high-crit Toons (like IG-86). I'd lobby hard to revert Advantage to its original state - criticals by themselves are boring, but Advantage synergies (like with First Order squads) provide more strategic options.
GW and Arena battles definitely last longer - several recent battles have just been slug-fests of hit point attrition. Definitely not as intense or satisfying.
Challenges do seem harder, but that's probably what is meant by "challenge." ;) I've had to drop a tier for a few of them, but not a big deal.
Love the new events - this is what I've like to see more of, especially as a way to earn cool stuff like ability mats or high-end gear.
Just my two pence. As with any major update, change takes time to get used to, so I'm trying to keep an open mind.