"Alien Nation" is a perfect examples of a well-executed spin off. The original James Caan movie was a decent buddy cop flick, but the premise really lends itself to long0for television; and there's some great character development here as a result. It's a good mixture of sci-fi and cop show, and the big themes - racism, slavery, xenophobia - are handled with subtlety. But the important thing is that you do grow to like these people, and it's a worthwhile investment.
I know that there were TV movies produced to settle the dangling plot threads, but part of me is still disappointed it was cancelled on a cliffhanger (Fox was still young; it didn't yet have a reputation for killing off quality shows).
A good show, nevertheless.
7/10