I played Broken Destiny on the PSP which wasn't IV proper, but it was a rebalanced version and it was okay, but I prefer III. I wish Namco had done their homework and cleaned up all the glitches in III because it could have been the high point in the series imo. I still prefer it to any of the others.
Still, I guess we'll have to see how V turns out. The series has been nosediving in one way or another since II, so hopefully they can pull it out of the shitter a bit.