8 is well worth playing, I think. I'm not even halfway through it yet, but I'm enjoying it a lot. Which is funny, because the first time I played it I also quit after some time, because I didn't like something about the game. Not sure what it was, because I think it's great now. Not up to FF7 standards though, but very few games are. Though speaking of that, Xenogears and Vagrant Story are both stellar RPGs that are well worth checking out, and that - in my opinion, at least - are better than FF7.

I though Infinite Undiscovery had an okay story and some really good characters and hilarious scenes. I don't recall the battle system very well at the moment, but it was okay or even fairly good. The battle system in Star Ocean is a lot better though. It's still kinda similar, and the games have a similar feel to them, but if that was your only problem with IU then perhaps Star Ocean is worth trying after all. Or at least worth renting until you figure out whether you like it or not.