If you can get a cheap copy of FFXIII then it's worth a shot. Many people out there don't like it but then again, there are a lot - myself included - that really enjoyed the game. You never know, you could be one of those that enjoys it, too, and you shouldn't let other people tell you that you won't. It's definitely one of the "bigger" JRPGs on the PS3, and a quick check on eBay says that you can get it pretty cheap right now. If you don't enjoy it, so be it, but hey, you never know until you try. I think it might come down to how seriously you take your video games... most of the people I know that really didn't like it seem to take their video games very seriously. I game a hell of a lot, but I'm also very laid back about it, so I can find enjoyment in things a little easier than most, maybe.

Of the other games on the PS3, I've not really come across anything "must have", but I will echo the mentions of PSN having some quality stuff on it.