Rather hilariously, I've already reviewed this book, and I hadn't realized it until I went to the Amazon page and saw my own review for it there! I will paste my review in and add a few thoughts.
In a twist on the usual fantasy story, Forward's heroes are not classically good-hearted heroes, but instead villains. Including an assassin, an evil sorceress, a greedy thief, and a black knight, the main characters are likable and intriguing. They band together to save the world from destruction by the powers of good.
In the beginning, I found the characters one-dimensional. However, as the story quickly unfolded, I was fascinated to see that both character introspection and interaction developed their personalities to an amazing degree. After that, even minor, short-lived characters managed to grab my attention fully.
There are a number of sly digs at other fantasy works, which make Villains By Necessity an even funnier book if you're well-read in fantasy novels.
I wrote that review in 2000 when I apparently was unable to actually remember plot points or characters from the book. Villains by Necessity does many things wrong. I won't lie to you. It's not extremely well written. There are many plot holes if you think about it too long. I think the author confuses the nature of good and evil with law and chaos (which is a no, no especially since the author is clearly a fan of early Dungeons and Dragons.) However, it's still fun if you're well-read in fantasy.
I can't really recommend that you buy it since it is rather expensive (having been out of print for ages), but if you know anyone who owns it, or if your library has it, try to read it if you like fantasy or Dungeons and Dragons. It's take on concepts present in most fantasy novels is interesting and refreshing.
I will admit that when I was younger, a particular favorite of mine included the skewering of Dragonlance that was more meaningful because I had just finished reading the original Dragonlance trilogy. Nowadays, I enjoy Sam (the book's main character and an assassin) and relationships with the other villains around him much more. The parody has become less enjoyable, but the things I considered boring at that time have become more. Such is life.