The two part show in London is excellent. Too many haters here looking for holes and sounding like bitter kill joys. The time travel plot which I normally am cynical of is perfect because it allows nostalgia and revisiting old memories at the same time of exploring new characters and stories. How they do the magic is literally magic. I also think the music and choreography is really tight. The perfect sequel to one of the most magical bits of my childhood.
I get some of the critique around how characters evolved (e.g. Harry), but people change over 20 years. Are you the same person you were 20 years ago? i'm certainly not. They are allowed creative license. Also it is theatre, so being a bit more exaggerated is part of it. Also part of what makes the books great is the characters are flawed - not perfect Hollywood do no wrong types. And that adds to it!