Let me just mention up front that I love Endless Ocean. My four-year-old son loves Endless Ocean. My husband and daughter think it is pointless. I am a very casual gamer, I rarely will play video games by myself. I am also not very competitive. So with that in mind, here's my review.
Endless Ocean is a single player simulation game. You are a scuba diver and your job is... well, whatever you want it to be. The game suggest several things you can do, but you can do what ever you want. There is no real tension in this game other than a few spooky emails at one point when you find a certain artifact. One review I saw said it is impossible to die, and I'd believe it. Basically, I explore, pet fish, and make friends with dolphins.
I think the graphics are really cool. There are fun areas to explore like coral reefs, underwater caves, and ruins. I like swimming around and learning to identify fish. The tasks the game suggests (via "email") are guiding people on diving tours, photographing fish, and various scientific research dives (ex: mapping whale migration paths). There is also an aquarium that you can stock with fish you identify. (The aquarium is a great place for a younger child to practice controlling the diver.)
This game starts off really slow to get you familiar with the controls. There are a lot of things you can do, and new controls are added after you complete certain tasks. When you start, all you can do is swim and look at fish. Fairly quickly, you make friends with a dolphin (who you can dive with and train) and get permission to do night diving. The slowness of the start almost turned me off the game because swimming around this one particular coral reef and petting fish is only interesting for so long. However, I'm glad they did start slowly because I would have gotten frustrated by all the different keys (remember, I'm not a gamer at heart). The slowness of the start allowed me to learn all the keys gradually and now I know what button does what.
How I play:
Me and my son play together, or rather he watches and points out fish I might have missed seeing. He gets frustrated very easily and this game, since there isn't really a score or anything, allows him to play and not throw tantrums. We start up the game and usually train one of our dolphins. This consists of giving the dolphins commands, shaking the wiimote wildly to tell the dolphin "go", watching the tricks, then feeding the dolphin as a reward. Then we go diving. We pet fish if we don't know what they are. We sometimes go diving with a dolphin and they point out hidden fish, but the dolphin is hard to keep track of since it is much better at swimming than I am at guiding the diver. My son likes looking at the encyclopedia of fish. Once we find a new fish, it adds it to the encyclopdia and my son likes seeing our progress. If we pet a fish enough, it becomes our friend (for the dive) and follows us around. I get lost easily, so learning to read the map was important.
I like this game. I find it interesting and relaxing. I like seeing the new areas, searching for fish, and playing with dolphins. If you are looking for a laid back game, this is a good choice.