Scifi recommendations

This is not so much a book review, as a plea for help.I like science fiction. Or, I should say, I like the idea of science fiction. In practice I find most of it deeply disappointing.I know the old adage that 95% of everything is shit, and that sci-fi is no different from anything else in this respect. But I'm often surprised by how terrible some of the 'great classics' turn out to be.I'm currently reading The Mote in God's Eye, which I've been led to believe is one of the all time greats. I haven't finished (no spoilers please!), so maybe it improves, but I'll have to be honest that my initial impressions are that it's really shit.Cardboard characters, a setting that shattered my suspension of disbelief right from the beginning, tedious writing style. The idea that engrossing fiction should show, not tell, is not a new one, and yet it seems never to have occurred to Niven and Pournelle. Much of it reads less like a novel and more like a sourcebook for an rpg.The discovery that scientists of the far future have a 20th century journalist's understanding of evolution is not unexpected, but doesn't improve my view of the book.So, having said all that, can anyone recommend me good scifi? There must be more of it out there. I promise not to complain if I hate your recommendations. Not much, anyway.

I've read a lot of Iain Banks, but oddly none of the books where he has a middle initial. I did enjoy some of his books, so will certainly give them a try. Slaughterhouse 5 is great, but I'm not really sure I'd consider it scifi. Kind of hard to classify.

The great classics rarely are, by definition. Publication date is not a concern.Recommendations noted. Ancillary Justice and the Culture novels got multiple votes, so I might opt for them.

The Foundation books were another in the line of supposed classics that disappointed me greatly, and I've never read I, Robot as a result. They struck me as Asimov more describing a concept than writing a novel.

I remember really enjoying Dune - are the sequels worth delving into?