Having just listened through this three-disc OST a second time, I can't say I see myself doing it again. Out of the whole three-and-a-half hour set, the reprise of the original Phantasy Star Online title theme "The whole new world" is the only track that particulary stands out. (Even in it the arrangement of some added electronic percussion leaves something to be desired, but the theme makes an impression at least.)
Granted it's a semi-ambient album so you can't expect it to make a huge initial impression thematically, but an ambient album needs at least some imaginative arrangement or creative sound design to make it interesting and this has neither. There's nothing particularly bad about it (except for a slightly tiresome string of higher-intensity tracks at the end) and as BGM in the game it probably suffices, but aside from people who've played the game enough for the generally forgettable compositions to sink in, I can't imagine anyone getting much enjoyment out of it.