Sypha and Trevor's romantic relationship seemed to come out of nowhere after the end of Season 2, but I liked that their interactions were sweet without being too "lovey dovey." It's clear that despite the occasional argument they deeply care for each other, as shown by Trevor's reactions whenever Sypha's in danger and how playful, comfortable, and fiercely loyal she is to him. I also thought Isaac's story line was pretty good, with him gathering an army of demons, interacting with a few humans that make him rethink his plan to carry out Dracula's wishes, that awesome battle with the old Magician and Legion, and gaining a few magical artifacts for his eventual confrontation with Carmilla's crew and Hector.
For me, the weakest storyline this season was definitely Hector's. It was always clear that Lenore was going to screw him over in some way, and no matter how charming or seductive she might have been I'm surprised that Hector ever thought running away together was a viable option. He was understandably skeptical and knew exactly what they were trying to do up until she called him "pretty" and slept with him. How is he that much of a fool? I also thought the scenes of Carmilla's "sisters" plotting how to build an empire were pretty boring, though I understand it's meant to be the set up for next season.
Alucard's storyline with the two Japanese vampire hunters was also a little slow, but it was a sweet look at Alucard dealing with his loneliness and trying to make new friends who eventually betray him and explain his disappearance until what I assume will be the Symphony of The Night adaptation. It was a real gut punch to see how much he enjoyed their company, and how much he was enjoying that threesome, only for them to betray him and force him into becoming more like his father.
Lastly, this season also had some really hype battle moments. Sypha had the best kills for the most part, but my favorite moment had to be when Trevor was struggling while battling the Soul Beast, that ominous church organ tune started playing, and he busted out the old whip for a Vampire Killer/Morning Star dual wield and eventual item crash.