Harman has a post up on the three best books of 20th century philosophy. He again makes a case for the Logical Investigations: Logical Investigations is the most underread and underrated of the three today. Husserl looks to some people like a relic, though I doubt he’s either more technical or less readable than Whitehead (who surrounded brilliant aphorisms with pages of blandness). But I would say that the real flaw of the book is reflected in (reflected in, not caused by) its parcelling out into six separate investigations: there are so many brilliant ideas in the book, but after finishing it you have to do a lot of organizational work in your mind to remember what Husserl has just shown you.
I’d have too crowded and esoteric a list to come up with the top three, but I know that one book not crowding the top three would be Logical Investigations. Perhaps it’s because I couldn’t imagine teaching it. It is simply numbing for hundreds of pages at a time, and I find that the people who came through Continental before me like the book mostly for where it points the way to Ideas I. And I guess people talk about the critique of psychologism. But I just couldn’t imagine, unless I was teaching a rabid bunch of Husserlians that I could ever pull off getting students through the sections, say, on color. It takes on so many debates (esoteric to the period and otherwise) that it’s hard to find a thread to hold onto by which to pull students along. (Telling students that it’s important because, as was told to me, it’s a “breakthrough” to the later work is really not enough: then why not just read the later stuff?)
That’s not to say I don’t have a soft spot for under-appreciated, supposedly long and tedious books. (I’ll see your Husserl’s LI and raise you Sartre’s CDR!)