To the surprise of almost no one, I really enjoyed Before the Storm! I was wary going into it because a prequel to Life is Strange sounded difficult to pull off (especially by a new developer) so I was amazed at the level of understanding they had for the characters. Chloe was basically perfect. One of my favorite moments was in BtS Ep1 in the junkyard where she starts smashing everything. I feel like a lesser writer would've just had her break down and cry when Rachel left, but that isn't how Chloe processes emotions. She responds to things by lashing out, so having her go on that rampage was the moment I realized these writers really knew what they were doing. I was also impressed with Rachel, who was excellent (especially since she would've been an easy character to screw up). They made it very easy to see how Chloe could describe Rachel as 'her angel' in Life is Strange, but they didn't go overboard and make her perfect or anything. She was flawed, and I was always left with a sense that large parts of her were an act, which was exactly what Rachel needed to be.
That said, the game wasn't perfect. I really feel like it would've benefited from having five episodes instead of three because the third one felt super rushed. I would've preferred one episode dedicated to learning about Sera rather than an info-dump, then one to learning about what Rachel's dad's role in everything was, and then another to wrap everything up. Life is Strange wasn't perfect either, though, and Before the Storm's problems were similar to it so I don't hold it against it much. I felt it was exactly what a prequel should be because, for me at least, it enhanced my appreciation for the original story. Seeing Chloe and Rachel together added a lot of depth to Chloe's desperation in LiS, and seeing Chloe here, at arguably her lowest point before meeting Rachel, really justified a lot of her actions in LiS for me. Stuff like that matters more to me than the problems I had with the third episode, so I rank Before the Storm at roughly the same level as Life is Strange itself! ---