This game is fan service all over again (like Dissidia). I'll give my full impression after having the Japanese version and putting in about 10 hours.
At first I didn't think too much of the game. I played though the five songs available from each FF game, and I thought it was OK. I sort of expected this to play like an overpriced iPhone game. While I was playing though, I realized I was getting crystal pieces towards unlocking stuff. They seem like other playable characters, but I can't say for sure yet (plus I'm not going to look online and spoil anything for myself).
Because I've put in over 200 hours on the Dissidia games over the past few years, I thought I knew the music inside and out. It turns out that wasn't the case. There are "new" songs from games I thought I knew, and stuff that's entirely new to me (anything FFXI). I just recently found out about the ability to unlock songs through the Chaos levels (challenge mode in English?) after clearing give or so, I realized I was hooked. This is where the game really gets you. You play random songs that are much harder than normal, but still not at expert level. It's perfect too, because after you beat the two random songs, another pair of random songs unlocks to play. There's and extra incentive to do well here though, as you can get rare item drops from mobsters if you get a big enough chain or beat enough enemies.
I've found that having Lightning and Cloud on my team really helps out. Cloud is my leader, and I have him equipped with power-boosts to slice through enemies, and Lightning has a 20CP skill (that's a TON of CP) called Libra (again, I'm playing the Japanese version so I don't know the actual English equivalent) that makes it do at the end of the second song you ALWAYS get a rare drop from a monster. No matter what my team is, I'll always have her on it for that skill.
Save for hand-cramp breaks, I say down yesterday and played this for hours when I realized how hooked I was. After every 500 song points earned you unlock a seperate sequential thing that's more or less another carrot on a stick that keeps you going.
There are other modes in the game that I haven't really tried out yet, but I'm really happy I finally got this after sitting on it for so long. The music is fantastic, the CG backgrounds on stages that have them work well on the cart (even FFXIII CG looks great), and it's a full-blown experience. If anyone out there thinks that this should have been a $5 iPhone game, you're missing out. I figured it would be that way, and I'm glad I was wrong. With three difficulty levels per song, nearly 50 downloadable songs (which are very easy to get), and random song selection in the Chaos levels, you'll be playing it for a while. At least I will anyway
The tapping tone can also be adjusted to off, low, med, and high volumes. I keep it at low, and I've never found it to be annoying in the least. Considering the fact that I play with earbuds in, I find that it keeps me with the song, in case I were offbeat...which is one thing the game and notes never are. I have yet to hit a note that I thought was kind of odd.
The only shortcoming the game seems to have so far is in overexplaining things before you start the game. It can get annoying, but of you don't need it you can just tap them away.