I got the game four days before its official street date. I've been playing it for about a half hour a day every day since then.
The gameplay in Nintendogs is a Tamagotchi with adorable 3D graphics, rudimentary touchscreen headtracking, and janky microphone support. The gameplay on a 1997-era Tamagotchi is more complex, actually, as they can age/die. Nintendogs just stay young puppies forever.
There are no "environments," beyond square, bounded rooms. There are no items that actually affect your dogs in any way beyond short visual canned animation loops. (I suppose that some of the sports items may change your dogs' physical endurance, but there's no indication of this.) There is nothing to "do" except feed/water/clean your dog, toss it some toys, take it for walks, and throw a frisbee / compete in "agility" dog show / compete in obedience dog show.
If I were reviewing the game on a 10 point scale, I'd give it at least an 8, maybe a 9. It's good, it's cute. But it's shallow. That's different from simple ... simple can be good. Shallow means that, honestly, there's not that much to do in Nintendogs. The game has no meat to it. As ThongyDonk says, you "get in what you put out," but the game is designed around severely restrained inputs.
It is a Tamagotchi with adorable 3D graphics, rudimentary touchscreen headtracking, and janky microphone support. And Famitsu has declared it a "perfect" game. A shallow puppy poking sim -- not "raising" - that implies some sort of change over time. And, like a Tamagotchi, Nintendogs is virtually guaranteed to wear out its welcome in a few weeks. That's why I'm in such disbelief.