It's worth noting that
The Foundation Trilogy was mostly a set of short stories published one-by-one between 1944 and 1950 in
Astounding Magazine. And because of the changes in settings, time periods and characters between most of those stories, not one of those books is really going to read like a novel. Especially when the original trilogy covers almost 400 years. The book versions were published in '51-'53, and I remember them being extremely popular in the mid-70s when Avon re-published them in paperback and the single hardback was one of the staples of the Science Fiction Book Club (introduced in '63).
Someone earlier said "six" Foundation novels, but there were actually seven. Here's the list in chronological order of the Foundation universe, but there are big payoffs to reading them in the order written and published:
Prelude to Foundation (1988)
Forward the Foundation (1993)
- Foundation (1951)
- Foundation and Empire (1952)
- Second Foundation (1953)
Foundation's Edge (1982)
Foundation and Earth (1986)
There's also
The Second Foundation Trilogy by "The Killer B's", that for the most part fall between Forward the Foundation and Foundation:
Foundation's Fear (1997, Gregory Benford) *
Foundation and Chaos (1998, Greg Bear)
Foundation's Triumph (1999, David Brin)
And there are definitely fun times to be had if you happen to have read Asimov's Galactic Empire books and the Robot series (
especially the later ones).
I tried to read the Foundation Trilogy originally in '77, but gave up way too early (I was 11). But I tried it again in 1981 and I was hooked. Coincidentally, I bought Deluxe Traveller at the same time (having avoided it for years for some reason) and the two are inextricably linked in my mind for all time because of it. At the same time, I can see why anyone coming to it thinking it might be like the game Traveller would be disappointed. There are better books out there for that (Poul Anderson, EC Tubb's Dumarest Saga, Piper, etc.).
I think the stories in Foundation are good, but the series really kicks into high gear in the second part of Foundation and Empire. Damn, that was an exciting read. And at that point, you do start to get characters you can care about, though I must admit that even toward the end, Asimov wasn't a great with female characters (like so many of his age).
I've read the whole series and the Robot books probably five times in my 46 years. I can't say that for anything else, and I'd probably feel guilty about it if they weren't such quick reads. Yes, thin on characters, but the concepts are big and I still love the "haHA!!" payoffs at the end of each story.
There is one other novel that I think is worth checking out: Psychohistorical Crisis, a 2001 book by Donald Kingsbury. It is not an "authorized" part of Asimov's Foundation universe, but rather a deconstruction of it (or, rather, just the original Trilogy). It's set 2700 years after Foundation, and fills in a lot of blanks, brings the technology up to date and does a thorough examination of how psychohistory works... or does it?

It's a long book, but a different approach than The Second Foundation Trilogy in looking behind the curtain.
* Foundation's Fear is an
awful book and IMO not worth any time put into reading it. The other two are better and almost feel like Asimov wrote them, though not necessarily that he
would have written them.