Reading classic science fiction in the modern day will always require a shift in mindset to understand the *context* of the book. To some degree, this is true of any novel, but for books like 2001 it's critical. 
 2001 was published in July 1968. Only a year later, man would set foot on the moon for the first time, and science-fiction would become science fact. The circumstances under which ACC was writing, and Kubrick was simultaneously filmmaking, are not replicable. 
 I don't recall which edition of 2001 I read the first time, but this time around I was lucky to find a library copy of the millenial edition, complete with special introduction by Arthur C. Clarke. I think I already knew it, on some level, but that introduction was the first time I'd actually understood, laid out in black and white, that the ACC's novel and Stanley Kubrick's film were something unique--twins, if you will, in that they are two interpretations of the same underlying code, neither truly derivative of the other. 
 And now I should stop gushing and get on with an actual review of the book. 
 According to that introduction, the theme that sparked the story was a desire to explore mankind's place in the universe. Well, if that's the case, the novel manages it beautifully (complete mindwarp that it is). 
 Science-Fiction is well known for certain genre-specific "pitfalls" (for example, wooden characters, overly technical language). But it never indulges in these without reason. Characterization is often sacrificed in favor of broad ideas, and technical language--which ACC does very well, indeed the science has held up over the years--is critical to writing something that will stand the test of time and scientific advancement. 
 And so the things that might make me cringe elsewhere (long passages explaining HAL 9000's history, or the nature of cryosleep) are forgivable in the face of the beauty and the loneliness of space as seen through ACC's eyes. 
 To read 2001 is to step back into history, to gain insight into just what the leaps and bounds of spaceflight were doing to society. It seemed an upward climb without end, sparking questions about our purpose as a species. 
 It's not a perfect book. The first 7 chapters or so are head-scratchingly odd, and the ending is one heck of a trip... but even then, it's a good book. And more than a good book, it is a story that has become embedded in our cultural conciousness. That said... I would normally be inclined to give it 4*. But, between the fact that I really do think the world of this book and the more objective cultural impact of this story (in both forms), I'll tack on the 5th star.