I actually picked this book up without having read any of the Dragonlance novels previously. From my perspective this was the beginning of the story, not a prequel. This is due to my own ignorance of the order in which they were intended to be read. I have since read both the Chronicles trilogy and the Legends trilogy.
That being said, it was okay, not great. There is a lot of emphasis placed on the characters themselves, and not on the story of the book. I'm assuming, these novels being written after the Chronicles and Legends trilogies, in which Raistlin plays a huge part, that the characters were intentionally the main focus. If you read the originally series before this, I would think you would be much more interested in hearing more about Raistlin, and the origins of him and his companions, than reading another separate tale.
From my perspective, reading this first it was a good book and I would have called it just that; a good (not great) book. However, the trilogies that come after this are fantastic! These two novels simply add depth to an already excellent tale and are worth reading even if you have already read the trilogies. It is just like reading an excellent book, once in a while you will come across a less exciting chapter that may not be "great" but it adds significant depth to the rest of the story. If the Dragonlance series was one book, this would be that chapter, and it is definitely worth reading it to get to the rest of the story!
Side Note - I actually preferred reading these two before the trilogies, and if I had to do it over again I would read this first still, it just seems to flow better that way.