Though it started very slowly, the show has really hit its stride in the last few episodes. The aliens probably could have been featured earlier in the series, but I liked the development of the various characters in those early shows.
The acting is really well done all around, but the children who are led by Caspar are particularly good.
The only complaint I have is the lack of a suitable resolution for the Sam Neill episode that began the show. What the heck happened there?