I played Zoids Legacy when it came out for GBA (since it's the only english release) and really liked it. I've played it like 3-4 times since then too. It's a rpg with a rather lacking story, but the whole "zoids system" is really addictive and very fun, every time I play I can't get enough. If you're a fan of rpgs and play GBA games, I suggest you at least give Zoids Legacy a chance, the upgrading/leveling up/weapons systems are first class and will have you playing for hours trying to better your zoids. You can make new ones, change pilots, upgrade all kinds of stuff, etc etc etc...
This one doesn't look like it will be the same though so I guess I'll just have to wait and see...