Radiance is a game with a ton of things going for it; it uses a tried and true d20 base with an analytical look at how the core mechanics work in order to create a system that combines the familiarity and simplicity of the d20 system with a more flexible character handling system that not only reduces the difficulty of learning the system but also allows some pretty neat other things.
As far as the Players Guide goes, it has very high quality; it has more art and a more coherent design than an average free PDF, but it also has superb writing and contains a great amount of content. Its sleek and streamlined rules allow for a book that isn't terribly gigantic but still contains a ton of stuff for players to handle all sorts of situations, and provides an interesting insight to the setting, even though there's not a terribly high amount of connection to a setting within the book.
All in all, for a free game, Radiance is definitely stellar, and I'm seriously considering picking up a hard copy to have laying around should I have to run a game session without my laptop handy.
[5 of 5 Stars!]