It's pretty good. I do have some complaints though. I find way too much "Gee whiz!" in the UI. Everything doesn't need to be lights and shinies. I feel like Blizzard's relationship with Activision really shows in the MASSACRE! and RAMPAGE! bonuses.
There are some logical inconsistencies to me too with the way they've re-wired skills. Weapons, by and large, are cosmetic. When your primary attack is an ability which just translates weapon stats into a formula...it takes some of the "a sword is a sword" out of the whole thing, except for attack speed and how damage and some stat bonuses are tailored. But it's all layered through so many formulas that you kind of stop paying attention to what kind of weapon you're wielding. It kind of applies to armor too, since equipment restrictions have pretty much (except for some weapon types) been completely obliterated.
Leveling kinda feels anti-climatic too. (And has more of the "Gee-whiz!" goin' on.)
Not sure how I feel about skills and runes yet. My gut reaction is that it's a little underwhelming and has taken all the novelty out of a "build." The differences between characters now seems to come down entirely to gear. Maybe I'll find more to like when everything is unlocked.
Visuals are pretty outstanding though. There's lots of little things in each area to smash, open, loot or interact with. Of course, it's hard to appreciate much of it when you've got 3 party members destroying everything in sight.
Of the 3 classes I've tried, Monk is by far my favorite right now. Each hit just feels so satisfying. Witch Doctor is fun in a chill and relaxed sort of way.
The game feels....pretty damn easy on normal. The regularity of health orbs and the way they heal everyone almost functions like a backup AI healer. Potions are auto-consumed right before death too and it all just feels a little......idiot proof. At 1/3rd of Chapter 1, it's probably too early to tell. (And there are 5 difficulties.) Still. It contributed to a somewhat mindless bashing experience. I'm not sure I ever used a potion on my first run through, voluntarily or otherwise. I had a stack of 35 by the end of it.
I'll be buying based on the SP experience for sure. Despite what I don't like about it, there's plenty of good stuff going on.