You want great acting, go to traditional human scale material that elicits and accommodates it. You want giant sand worms, Death Stars, ray guns, robots, star gates, galactic empires, big ideas, and space ships doing battle with swooping sounds and dramatic orchestral scores, go with science fiction. If you want great or even just acting in science fiction, you are almost always asking for too much.
Which is too bad, because science fiction should depict a higher level of humanity we all can aspire to. But we all know who doesn't want that...