I imported a Japan PS2 last year, and overall I'd say it was an ok move on my part. The only game I really play on it is Pop'n Music, so in that aspect it was worth it. So far have 7,8,(9 in the mail) and 10. (What's funny is, an arcade here has Pop'n, but I'm so used to the tiny home controller that I prefer the home version as opposed to the real thing.)
I also have Zombie VS Ambulance and Oneechabara 2. It was actually Onee that convinced me to import, seeing a chick in a bikini killing zombies put me into a rage. Sadly both games are pretty hard, and I've never really gotten the hang of it. I've learned to just stick with games that have hardly any reading involved, safe games like Pop'n.
Anyways, to get more on topic: When it comes to odd genre games, I'm always on the lookout for anything cooking, and most music games as well. Cooking Mama I thought was terrible, but Ore no Ryori is a treat if you can play it! It's a cooking game on Psone.
Also, Princess Maker 2 is similar to Monster Rancher, especially part 1 if you've played it, the style and training.