There are many different genres of sci fi. Seveneves is pretty much hard science fiction, in that it deals with plausible physics, which is also one of my favourite genres. I particularly recommend the Xeelee Sequence (a series of novels) by Stephen Baxter if you like mind bending sci fi over cosmological time). More classically, The Foundation series by Isaac Asimov is a great (and shorter) read. First contact novels can also be interesting (meeting aliens for the first time). Rendezvous with Rama by Arthur C. Clarke is great. Also, Blindsight by Peter Watts. So many others!
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