I'm a huge ZOE fan. You really don't need to buy the first game, because you can watch the ZOE1 story cutscenes in "The Second Runner". I own the 2nd game and a Japanese special edition I got for 1000 yen, plus the GBA SRPG and the entire anime series.

ZOE 2 is definitely the best on that list, and my top pick.

If you're gonna go with Xenosaga (hint: Don't) you have to get all 3 of them. You can't really just jump in at the end and expect to 'get' everything. I say skip it entirely, and if you're at all interested in the crazy story read it up on Wikipedia.

Haven't played Tales of the Abyss yet, but I've played a few of the previous Tales games. Tales series has one of the more interesting combat systems in any RPG I've played, so I'm sure it would be a good buy.

Rogue Galaxy is just fine. Nothing particularly special about it, but it's not bad at all.

Still, you have ZOE2--which I agree with Ookami as being a Generation Classic--against other less-than-outstanding games. If I had to rank them 'in order' to buy them:

1: ZOE2
2: Tales of the Abyss
3: Rogue Galaxy
4: ????
999*:Xenosaga III

I don't like Xenosaga :P