I was on the Wonder in November, will be on the NCL Dawn this coming November and then the Magic in April 2005. Other than price, some of the things I am already aware that is different - 1) most cruise ships have casinos -
DCL does not, 2) at least in the case of NCL, the kids club hours are much shorter than DCL's, 3) on NCL you do not get "free" soft drinks at dinner time as you do with DCL, 4) cabins are smaller on NCL than on DCL, 5) no split bathroom on NCL as opposed to DCL - there will just be 2 of us on the NCL trip so that's not a problem for me, 6) it seems that most other cruise lines have salt water pools - DCL has fresh water pools - not sure if that is a plus or minus or makes any difference at all and 7) as other cruise lines seem to attract an older and/or couples with no children, by looking at the Navigators for both lines, there does seem to be more adult only activities than on DCL.
I think you will love your DCL West Coast cruise - especially if you have young children! We will probably cruise DCL every other year and try out other lines in between.