Curiosity got me and I bought the game together with my mother. First impression (played the first mission, maybe 10 minutes) wasn't so good, for a game about observation it's not very pretty, the environments look like low Gamecube or PS2 level and the animation is very mechanical (especially the dolphin and penguin I saw looked like crap). Interacting with the fishes is very limited, you can poke them, stroke them or grab them but the ones I saw didn't react in any way, the only way to tell you did anything was the icon that showed up. No flinching, no looking around, nothing. Only feeding got them to react. You have to "level" your interaction with the fishes by repeatedly doing stuff with them to unlock better levels of description for them (without level 1 you don't even know their name). Says poking and stuff takes higher levels too, maybe the fishes will start to react at a certain level. Of course the humans look ugly but that's not the focus of the game anyway. There's limited character customization but you aren't told what the options will look like before you pick them.
There are missions and hints around to guide you to interesting spots and of course a completion list. Controls are reasonably easy though it took me a while to figure out that stroking is done with a shaking gesture instead of moving the pointer over the fish. Easier to navigate underwater than in Super Mario Galaxy.
When on deck you can sit in a chair and look at the sea, would have been nice if swimming to the surface also moved the camera above the surface so you could look around.