The Monster Rancher series, especially the first two editions, are very beloved by those who were fortunate to play them at the time. At first glance you may dismiss them as Pokemon-clones, but that would indeed be a great disservice.
Combining a stat raising system very similar to the one used in the Princess Maker series of games, and a arena battle system, the game offers a great deal of complexity and replay. A wide variety of monsters to raise, unlockable content, and the original shrine's CD generation made for a great game that was overlooked by most of the playstation crowd at that time. For many of us who found the Pokemon games monster raising to be too simple, these games had the depth and detail we loved.
The DS version is very like these two versions in style and game play. I've been waiting for a US release of the game since the DS was announced, and it was a contributing factor to me buying one in the first place.