The core problem is that good sci-fi needs someone intelligent to write it, and nearly all scriptwriters are, shall we say, not entirely equipped to fulfill that criterion. In fact, scriptwriters learn early on that 99.999% of any audience is essentially brain-dead and just wants empty spectacle while they chow down on snacks and fizzy drinks. So looking for good sci-fi is like looking for Bigfoot: you may be convinced there's something out there but you're highly unlikely ever to find it. All these years later, the Kubrick/Clarke classic 2001 is still the benchmark than no other film or series has come remotely close to approaching. The best sci-fi is still contained within Einstein's original thought experiments (albeit he got a couple of things a little askew).