1 life, 1 planet, hundreds of ballpoint pens

I was reading Hitchhikers Guide to the Galaxy (time number 3) on the train platform a couple days ago. I was pretty much lost in the book, when some guys I didn't know came over, to strike up some pleasant conversation about "How fiiiine you look, but nah nah nah for me, my fren ova there thinks you lookin niiice girl. You got a boyfreeen?"Anyways, I sort of ignored them completely partially becuase most of that sentence was not english. This, which they thought to be profoundly rude, triggered one of them asked me what my book was about and "why it so good you can't even talk to no body, en gid no loove to the main?" before walking away. Which sort of got me wondering, why was my book so good? And WHAT was it about?
I guess you could say the book was about a man who lived on earth whose alien friend saved him before the planet blew up and ten lead him on multiple misadventures to other planets and in other spaceships with a comical cast of aliens such as Zaphod Beeblebrox, and Marvin. Then they discover the infinitely large planet on which planets are created, get in some trouble with genius mice... and I don't need to go on.
But that sort of doesn't capture any of the wit and well writing. Plus with a story like Hitchhikers Guide to the Galaxy, there's a lot more. It's like there's a hundred plots, not just one. And to answer why it was so good... There's a number of reasons;

• The writing is so witty
• It's random- but not in the obvious trying to be random sense
• It's never boring
• It's hard to keep up- no matter how many times you read it
• Its So funny- which should count as like 4 points
• It's spacey-futuristic without being nerdy or lame
• All of the space stuff makes sense ^ not like a magical never ending pony lazer beam that runs on tears (I actually read a book with that in it)
• It's So funny
• There are tons of little side stories that are as interesting as the main ones. (Like Veet Vojagig and his quest to find all the ballpoint pens hes ever lost)
• Its So funny
• The names are lame in an amazing spacetacular way - Veet Vojagig, Trillian, Zaphod, and Slartibartfast.
• It's real sarcastic and witty in a deadpan sort of way
• It's... So... Funny

 And of course, it has an interesting main plot. But still in all of that list, I havn't even begun to think of all the things that make my book good... What do you think? What makes a book so good? Or so bad? That's right... I challenge you to think and respond.