Singing a good melody
Ar tonelico II was certainly an experience from start to almost finish, and it took me around 65 hours to more or less 100% the game (which I always aim to do when playing RPGs, unless they just flat out stink). The very very long, and sometimes complex, story however is probably its biggest flaw. At first it kept me interested, and I patiently read through the (sometimes) extremely long conversations, even if most of them are without voiceacting (in the US version at least). Throughout the game I'd say around 5% of all conversations are voiced, and towards the end of the game where conversations are, frankly, insanly long I just found myself skipping through them. It's like watching a movie without sound and just reading subtitles, and it really didn't appeal too much to me.
The second flaw would be the graphics. Sure, graphics aren't everything, and especially RPGs can often survive without fancy stuff. But most of the game are 2D side-scroll-like graphics, and it sadly is quite a pain to the eye. It looks more like old games like Chrono Cross and Final Fantasy to the SNES, and the pre-rendered characters have around 5 facial expressions. When you sit through a game that last 50+ hours it really doesn't help when everyone look the same more or less from start to finish.
Enough with the bad stuff! In short, even with a semi-bad story and outdated graphics, Ar tonelico II was fun. I wouldn't sit through a game for 65 hours if I didn't enjoy it; I would rush through it and get it over and done with as quick as I could. Nevertheless I found myself compelled to finish all the sidequests, crafting, and everything else before I fought the final battle. I doubt I'll re-play it anytime soon, but I don't regret putting all those hours into it. Especially the combat-system, once you get into it, is loads of fun, and the longer battles towards the end of the game are really the points when Ar tonelico shines.
So in short, if you enjoy a long-ish RPG with a great combatsystem, crafting, and ain't afraid of sitting through long conversations with 1995-style graphics, this is definatly a game for you.