The first Zone of Enders was released early in the PS2's life. It was released by Kojima studios, and came with a playable demo for the, at the time, in demand and much sought after, Metal Gear Solid 2. The public at large bought the game for the demo, played the hell out of it, and never paid the actual Zone of Enders title any mind and most ended up using it as a coaster.
This is a shame because the First Zone of Enders was a good game overall. The boss battles were great, and the control scheme was fresh and new, and made controlling a mech very fun. Not to mention it looked incredible for it's time, and is still a damn good looking game. The game was poo poo'd due to it's having only three enemy types, repetitive levels, poor voice acting, and it was incredibly short.
The second Runner on the other hand, took the control scheme, ironed out every flaw it had, made the gameplay faster, Jehuty (the main mecha) super powerful, and basically gave you enough weaponry to blow the shat out of everything. The bosses were even more incredible, more fun then the majority of MGS's bosses, and there were many more enemy types this time around, and more ways to blow them up, or slice them to pieces. The game had a great sondtrack, and the graphics were so hot they've been accused of causing global warming. The script had a Engrish translation feel, and the acting was even worse, but Zone of enders 2 still ranks as one of this gamings generation defining classics.
Too bad people associated Zone of Enders with Metal Gear Solid hype. And when Second Runner hit with no MGS anything attatched to it, other than mecha designs done by MGS artist Koji Shinkawa and Kajima's name attatched to the project, people ignored it all together. There was a altogether really good anime series, but when Second Runner was ignored the entire franchise was discontinued.
So yah, thats my rant on Zone of Enders, if you ever come across ZOE: Second Runner, buy it then and there. Its one of the best games you will every play. As for the rest, Rogue Galaxy, Tales of the Abyss, and Xenosaga III are all on my "To play eventually" list. The tales series has a great pedigree, though I wish they'd get with the times and release their games with a option to hear the japanese voice overs. Rogue Galaxy I hear looks great, but I also hear it has a story that runs hot and cold so I'm not in any rush. I'm a huge fan of the whole Xeno mythos, so I will be definitely checking out XS III sooner or later.