I can't believe there are so many persons that doesn't like the Foundation saga. This is my short review.
I bought the first book, I started reading and I just couldn't stop, for arround 2 or 3 hours I kept reading untill I finished and I run to the bookstore to buy the rest. Of all of them, I believe "Foundation and Empire" is the worst. I never liked The Mule and the ending is a bit artificial. But the rest is awesome... the psychohystory is awesome. Someone mentioned but I'm going to do it again:
The first three books where written as short histories published separatly in magazines. The rest where written as novels. What I like of the first three is that they are more about civilizations than about characters. In the first one, the characters, that is, the persons appear for very short periods of times and the real star is the civilization or the science holding up a civilization (when the civilization doesn't even know). The last two books are more in the style of Clarke from my point of view, and I like that a lot (Clarke was my favourite writter untill I've read Foundation, now I can't decide). I love the end, with robots, gaia,
GAIA!.
About the prequels, I bought them and they where in my shelf for a long time, I like moving forward, not backwards, so, I wasn't very intresting in reading 'how it began'. But some day, dying of boringness I picked them up and started reading. Once again I couldn't stop, it was so deep. The explanations of psychohystory and how hard it was developed, it was awesome.
One thing that I'd like to read is the foundation-sequels written by another persons, not Assimov. I was adviced against it a lot of times, but I also see a lot of people not liking Assimov's original work, so, I may also like that other work.