The collections are pretty impressive for the genre. They have some cool costumes and props from movies and shows like the Twiki costume from Buck Rogers and a great collection of Star Trek weapons and even Kirk's command chair from the original Enterprise. The best part for all of us was the Spacedock, a super well done exhibit of famous spacecraft from different sci fi shows and movies. It really felt like we were looking out on a spacedock; the displays they used for more information were super well done too with these slick dual layered displays. Hard to describe; worth seeing.
As a family, it was only OK. As I've mentioned before, the boys are crazy about Star Wars. There was just enough Star Wars stuff in the museum to keep them from totally rebelling against the visit, but much of the place was dedicated to science fiction from my generation and earlier. What's more, there are very few interactive displays, so kids who can't read much yet (e.g. Michael) or have short attention spans (e.g. Andrew) will not find the place very interesting. The whole place is unnecessarily dark and a little spooky too. I think it would have been more fun to be there by myself, frankly, but even then.
While we were at SFM, Michelle went to check out the DoubleTake show at EMP. (I had taken Andrew to see this with his class a few weeks ago.) This is a showing of some of Paul Allen's private art collection (doesn't everyone have Monet, Lichtenstein, Degas, Rothko, Picasso, van Gogh, etc. hanging around their home?) While the pieces themselves were great, the interesting part of this exhibit is how they have the art arranged. They've paired (in some cases tripled) art together to illustrate some theme, either contrasting treatment of simliar themes or showing similarities across eras and artists. I've never been good at viewing art, but this was a great way to get me to think harder about what I was seeing. (Loved Richter's Candle.)
Neither the SFM or DoubleTake exhibits were very large, so you could easily to do both in a morning or afternoon. In both cases I felt that while there was some amazing/interesting stuff and the exhibits were well done, these weren't great values. They're definitely not great for families with little kids. That said, if you like art at all, go see paintings at DoubleTake. You're unlikely to see so many paintings from such prominent artists in Seattle again.