The feels I have for this franchise - ZOE slipped in between Konami Work on Metal Gear Solid and then got completely forgot about and if I am honest...I actually loved these two games more than almost any of the Metal Gear Solid games.
Zone of the Enders. I've got to say that I love the series though I'm not sure for what exact reasons. I originally bought both games in a Sale for £2, came home and played through both of them in a day. The first of the two games is a bit simple and uses some mundane tasks to build on the games lack of variety but I would say it was good since it gradually got better towards the end and has something a lot of Mecha games fail to have/build on, character. Zone of the Enders 2 then builds on the story and focuses more on moving things along with some improvements to the combat. Both have little faults but they're good. If I was to say which version you should get, I would say "the originals on the PS2 if you're into retro things" or "the PS3 version because it looks and plays a lot better than the 360 version which is still bugged and suffers from frame drops" if you care more about graphics.