Last Call is about the occult and symbolism, threaded through history, actual famous people, the Vegas culture, the world of gambling and card games, Tarot cards and so on, filled with action and fringy characters. Tim Powers has put a lot of effort in the research and the details and that, ironically, may be the problem of this book. There are too many characters, too deeply rooted into the mythology of chaotic gods and the significance of cards, doing things that you need to reread a few times in order to understand. It gives the book a hallucinatory feeling, like you are there and not there at the same time. This might help people get into the atmosphere or push them away.
The book is also quite long and just the first of a trilogy. While I've enjoyed living in the world described by the book, and while it is well written, I also found it a chore to read. That doesn't mean it's not a very good book, it's just that I don't think I was its intended audience or maybe reading a few pages before going to sleep or listening to it while walking the dog were not the best situations for getting into the story.
Bottom line: very interesting concepts and well written, but requires effort from the reader to fully enjoy. I found it a bit too long for comfort and the pacing was a bit unreliable, too. If you're into symbolism and Tarot mythology, this might be the book for you.