NOTE: If you have not read or watched the book/show A Game of Thrones and do not wish to read spoilers, heed the spoiler warnings. This post WILL contain spoilers.
A Game of Thrones by George R.R. Martin was an excellent book. I watched seasons 1 and 2 of the show before getting into the book series, and I am a HUGE fan of the show. I have fallen in love with the books, and find them to be even better than the show. My "review" here will be comparing the book and the show.
SPOILERS: To put it simply, A Game of Thrones is about a fight for the Iron Throne; a throne that rules the seven kingdoms of Westeros. There are many claims to the throne, and wars are being fought to claim the throne. There is much more to the book than just war, however. Each character is complex, and the book is seen through what happens with several characters. There are several storylines going on at once, but it is written so masterfully that you never get lost or confused. The characters are so well developed that you grow attached and love them, hate them, cry when they die, etc. It is an extremely well written book,
The first book and the first season of the show are very similar; the first season stays very true to the book. There is a bit more about Lyanna, Ned Stark's late sister and Robert Baratheon's "true love", and the characters are a bit more developed. Joffery is even more horrendous in the books, in my opinion; he often has Sansa hit by his guards, and is much more angry in general. There is also something between Petyr Baleish and Sansa in the books that I don't recall in the show, (to me it seems Lord Baleish is a bit smitten with her, most likely since he could never have her mother). The Hound also seems a bit fond of Sansa. I think Arya is a bit more badass in the books (but a lot of this is developed more as the series progresses. She is a spunky little kid!) You see more into the prophetic dreams that Bran has in the book, though they aren't really explained as such. Dany is of course and lovely as ever, and you get to see more into her and Viserys' past. Overall, I would rate this book a 4/5. (The next book, A Clash of Kings, is just INCREDIBLE, therefore A Game of Thrones gets knocked down a point. The second season of the show also differs from the second book in some respects. Would anyone be interested in A Clash of Kings review?)