I remember seeing this movie as a kid, and I loved it even then. I was a fan to the Casper cartoons, and to me, this was a great movie. As a kid, it was just entertaining. Looking at it again as I am older, I now love this movie more than just because it's about my favorite friendly ghost. This movie does a good job clenching the issue of death and either letting it go and hang onto it as a ghost with unfinished business. The atmosphere, although often times comical (which is how it is with the cartoons too XD), has a really deep and emotional air to it, as we look at Dr. Harvey and Kat's loss at the wife/mother's death, as well as Casper's mourning for his life and loneliness as a ghost. The music itself is very beautiful, and the set gives a perfect background for both spooky and sentimental moments. If you're one who is looking for a good emotional ghost story, this is a great example, even though it was based on a cartoon. If you're looking for something comical, well, the three ghosts Stretch, Fatso, and Stinky are there to provide laughs, as they really do seem to be having a ball being floating ethereal beings capable of shifting themselves into horrific (and hilarious) shapes.
I don't remember much from the Casper cartoons, but it's not like you can totally base an entire movie on just those. The plots for the cartoons vary, and this movie could be counted as some sort of canon, I suppose. Either way, it does a good job capturing the lonely, friendly ghost that is Casper on the big screen (and TV set).
Go ahead and rent the movie; I'm looking forward to searching for a DVD for it so I can watch it again and again. I love it. I totally recommend this for everyone, kids and grownups alike.