I didn't like how slow it started at first, but now it's okay. I loved all the fight scenes we got so far, really showing off how greatly the animation has improved. And yeah it's nice that Ren and Nora finally get their backstory shown, and with the next 2 episodes they will probably get some more character development too. I really hated that cliffhanger at the end of the last episode though, it just makes me way too excited for the next episode xP, but at least we know a completely mindblowingly awesome fight is just around the corner, probably.
Volume 3 was my favorite so far too. It had tons of fights, really improved animation and a lot of plot twists and reveals that made it so exciting to watch. I don't like how in Volume 4 Cinder, Mercury and Emerald just instantly lost their entire villain status, and seem to be completely replaced by villains that really haven't done anything so far and most likely won't do anything else this volume.