NOTE: I am reviewing the game with no Pokemon DIamond, but I will rate it as if I had the game and as if I didn't.
The point of Pokemon Ranch is to really just transfer Pokemon into the game. Something comparable to Pokemon Box. However there are a few other things added. For one thing, the Pokemon interact with one another and do activities. However it will at one point get boring. Before that though, I'm sure you will be taking pictures of each little thing that happens with the new camera feature. You can send it to an SD card or the Message Board.
The care taker is a person called Haily. If you have Diamond or Pearl, she will ask you to bring her a wanted Pokemon within a certain time. She will give hints to find it and might trade with you for it with another Pokemon. If you don't have Diamond or Pearl, Haily will give you a few Pokemon every week or so. However with no Diamond or Pearl, the game isn't the least bit decent.
The graphics are colorful but are very choppy. However there is a charm to it. The music is good but not great. You won't be taking any interest in that but the tune might get stuck in your head.
Overall it is a decent game with the DS. But with no Pokemon Diamond or Pearl, it is a horrible game. It would of been better if it had more to do than just a box, camera, and help with Pokemon on the DS.
With it Diamond or Pearl - 7.5
Without Diamond or Pearl - 2.0