Stephen Poole has released his excellent book “Trigger Happy” as a free download, licensed under Creative Commons: http://stevenpoole.net/blog/trigger-happier/#more-159
It is also available from http://stevenpoole.net/trigger-happy/

"From the design standpoint, I haven't seen any better history of the game industry, and more importantly what that history means, than Steven Poole's Trigger Happy. Poole looks inwards, not outwards, not so much at what games do but at what they're about. The book is witty, well-written, and thoroughly-researched [...] I don't agree with all of Poole's conclusions, but that's all right: I admire the breadth of his vision and his willingness to wear his heart on his sleeve." Ernest Adams, Designer's Notebook, Gamasutra, Feb 2005

Trigger Happy, originally published in 2000 with the subtitle "The Inner Life of Videogames", is a book about the aesthetics of videogames: what they share with other artforms, and the ways in which they are unique.

Some excerpts:
What I've learned from gaming
Why games are like boring jobs
Moral maths
Cosmetic and functional space
Existentialism
On murder simulators
Political subtexts in games

I haven't read all of these yet but thought they may be of interest.