Nemo is a fatihful adaptation of the film only your children could enjoy.
In terms of gameplay, it's quite simple. You're mostly just swimming around. You swim through bubble rings to earn star rings which increase your turns at the mini game, and swim around while trying to complete your objective. There are two levels which is in first person and have you swimming through rings which are the irritating levels of the game. If you're used to inverted controls for combat sims, you'll be spending way too much time getting through them. The game looks very good, overall. It's bursting with vibrant colors and is quite reminiscent of the film. The still images of the plot look very nice. The sprites for the fish are very well done as well as their animations.
The sound effects are okay and the music isn't too bad. It's pleasant enough and certainly has you thinking of water. It's what you'd typically hear in those marine documentaries. Overall, Nemo is a bit too easy for the older crowd for it to warrant purchase. The levels offer little challenge and begin to feel tedious and way too large as you progress and the first person levels can be a pain. The game can be finished in a day and there is no replay value whatsoever unless you really like Nemo. If you liked the mechanic of being a fish and swimming around the ocean, you might want to look into the Ecco the Dolphin series. They are a much more challenging alternative.
For the kids who liked the movie, they'll probably get some enjoyment out of this game. It's quite more likely for them to replay this game.