Trying to fit another person's tastes is always difficult, so take what I suggest with a grain of salt (or a boulder).
John Brunner - Shockwave Rider - cyberpunk before there was cyberpunk (1975). You can't get any more outsider than Nickie Halflinger...
The Works of Cordwainer Smith (Paul Linebarger). Total output 36 stories and one "novel" (actually 2 linked novellas). Unlike anything you've ever read...and very, very, good.
Alfred Bester - The Stars My Destination. An unfolding flower of a book.
Jack Vance - The Demon Prince series. (Not Fantasy, far future space opera) Not open ended, 5 books with a definite ending. Star King, the Killing Machine, The Palace of Love, The Face, The Book of Dreams #1 and #3 aren't the best (but read #1 anyway for the intro to the series), #2, #4, and #5 are superb.
And I can't resist throwing in a couple of Heinlein Juveniles - The Star Beast and Citizen of the Galaxy. Big Ideas, expertly handled.
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