The Hitchhiker's Guide to the Galaxy - Douglas Adams "There's an infinite number of monkeys outside who want to talk to us about this script for Hamlet they've worked out"
Arthur Dent wakes up to find a construction crew outside his house, waiting to demolish it for a bypass. Little does he know, a Vogon construction fleet is outside his planet, waiting to demolish it for a hyperspace lane. Fortunately, Arthur's friend, an alien from a planet in the vicinity of Betelgeuse, Ford Prefect, lends a hand and the two hitchhike away from Earth moments before its destruction. This is their journey.

I Liked:
The Hitchhiker's Guide to the Galaxy is a classic, the perfect blend of comedy and scifi fun. Adams is acutely aware of scifi stereotypes and what makes people laugh and has blended them to perfection.
Our protagonist/hero, Arthur Dent, is a complete deconstruction of the "hero", the man who can elbow his way into everything and come out on top with ladies fondling him. Arthur is completely at the whims of chance and his friend, Ford. It's delightfully funny to see his reaction to being the third most intelligent life form on Earth and how positively useless he is to the Heart of Gold.
Ford Prefect is a delightful "sidekick", who ends up being way more helpful and useful than most sidekicks. It is he who saves Arthur Dent, it is he who attempts to find ways out of scrapes, it is he who sticks his neck out on the line.
Zaphod Beeblebrox is a kick in the pants to those who are interested even passingly in politics. I find it a riot how his job as president is to focus attention AWAY from those who have power. My absolute favorite line of his is "If there's anything more important than my ego around, I want it caught and shot now."
Trillian is your stereotypical damsel in distress/buxom lady, only she isn't either. A passing comment suggest she may be a physicist and a mathematician--far better than Arthur, whose only job is to "whine about Earth" (my poor attempt to render the book's words) and restate the obvious. She is competent, adventurous, smart, and not another objectified woman (though she certainly wasn't ugly, her beauty is not the primary attribute she has).
The story seems rather simplistic, but I found it a riot, which is what I believe was Adams intent (that, and a satire to our world). Arthur worrying about his house being destroyed when Earth is minutes from destruction makes him seem rather petty; seeing Zaphod race after Magrathea for the sole purpose of fame and money shows his shallowness and makes a funny statement to our constant pursuit of the purpose of life. Having mice manipulate humans shows how we are so eager to make ourselves more important than anyone else and our inability to see out of the box of our self-importance.

I Didn't Like:
The ending is a bit abrupt and kind of hokey. But then, you really can't critique the ending, given what the purpose of the novel is. When I listened to the audiobook, I found it challenging to figure out the Hitchhiker's entries and the story.

Dialogue/Sexual Situations/Violence:
Mild profanities.
Trillian is Zaphod's girlfriend and travels with him on the Heart of Gold. Arthur attempted to go after her, but Zaphod whisked her away.
Earth is destroyed. Vogons torture people with their poetry.

Overall:
If you want to laugh, if you like British humor, if you have read a lot of cheesy/70's scifi books, you need to read this book. Heck, if you like to laugh and like scifi, you at least need to try this out. It's funny, it knows what it is picking on, and it is clever. I also recommend listening to the audiobook where Douglas Adams himself reads the book. It's a delight to see how the author intends the book to be read.