I'm late on the bus for this, just bought the DVD for the kids, but DAMN what a terrific, SMART movie. Wow. Great on all levels, but the real stand-outs are the kids (THESE kids are PERFECT) and the script. It feels like it was written by these kids (in the way they speak to each other).
"Go get me a juice box, beeyotch." My six year old's favorite line. The movie is filled with great, real dialogue by these kids.
The F/X are good and all, and the story is neat, but the kids rock. The older sister is spot-on in her role, the middle kid certainly gets it right, and the youngest boy is also perfect (yeah, he's cute as a button and all, but not annoyingly so).
Dax Shepard is also terrific as The Astronaut, and Tim Robbins is fun as the Dad (a small, but well-written part for him). It's really cool that the movie rests on these five shoulders (no other cast) - and most of it is on the two brothers.
It's a shame when a movie like this gets practically ignored and stuff like Harry Potter & Chicken Little rule the box office. Not that they are bad, but Zathura is a real stand-out, and among my favorites of 2005.