I'm finally finished and can comment! I felt the book dragged in places, but really picked up when Lestat left Paris, and Marius's story was my favorite part.
I do think that the differences are because Lestat is genuinely a different person in this novel to Interview.
I agree with this, and he's almost been "Mary Sue"'d in some ways. Now he's responsible for the Theatre des Vampires and brought about the modern style of living as a vampire. The Queen awakens for him. I liked the character, but he was made a little too perfect.
The book had a lot to say about the meaning of existence, or lack thereof. Lestat has his crisis as a mortal over this, and then most of the vampire section also brings this up time and again. Lestat's creation as a vampire seems without meaning. The Paris vampires lose their purpose and have to find a new one. The ancient vampires felt their purpose was to be gods, to deal out justice and wisdom. Marius finds meaning in keeping Akasha and Enkil, and in his interest in witnessing history. But he admits at his story's end, "life does not need us. I have never had a true purpose. We have no place."
For all Lestat's angst, at heart he is a hedonist, and so is able to stop searching for meaning. But I think that caused some of his mistakes with Louis and Claudia, in his inability to grasp that they needed a meaning to their existence.
So, Lestat is close to his mother. Really close. And, it seems, he's unusually connected to the living for a vampire. She's also dying from a consumptive like disease. He decides to turn her into a vampire - admittedly with her desire - in order to save her life. Their relationship afterwards is a bit unhealthy.
This rather strongly reminds me of Spike and his mother. Though, as this came first, the other way around. This does make me wonder if the S7 writers were so utterly strapped for original ideas that they took inspiration from this bit.
I was struck by this, too. It's also similar in the way that both mothers fully embrace their vampire nature from the start, whereas their sons cling to humanity.
When searching for this thread, I found a 2003 thread about a musical adaptation being proposed by Elton John! According to Wikipedia, it actually did show on Broadway, but didn't last long.