For example, Neal Stephenson's latest (seveneves) was brilliant. Up till the last third, which was... boring.

Most scifi is quite frankly more on the boring side than on the intelligent, thought provoking side... But I use it mostly to test ideas against my knowledge of physics (which of course, isn't as good as I'd want it to be, but I have picked up a bit over the years). Unfortunately, the whole field seems to have taken a hard turn towards the more softer sciences, like biology and psychology, and other even less interesting stuff.

You can still find good things, though.