I own and have played both games, and I must concur with your assessment. While both games are working from the same formula I couldn't help but feel that Star Ocean took the formula for the most part in the wrong direction. The formula itself wasn't very great to begin with. Basically it was based on a structure of massive add on with no real implementation. All the aspects of the games such as crafting, collecting, upgrading, equipment, and the inventory are almost entirely irrelevant to the game. They are there, but they are hardly worth the time to play with.
The difference between the games is that while both have mountains of this content to interact with, and mechanics to tweak for modest or no real gain. Infinite Undiscovery was actually bothered to have an objective based game underneath. Which left the game being more or less coherent. The story meshed with the game, and the experience was always changing through the entire game. The fact that the story was not overdone, and the dialogue wasn't so terribly cheesy helped a lot.
Star Ocean suffers from redundancy on the other hand. While it is true the combat is much more complex it is not complex enough to avoid being a case of been here done this a hundred times. The combat it just not dynamic enough, and it rarely changes up the situation. Even more of a let down is the fact that for everything the game funnels you right back into instanced combat. There just isn't any variety. Even unlocking blocked chests is a chore as you have to take up to thirty or forty minutes to backtrack through the same areas only to accidentally get sucked into instanced combat with enemies that are far to inferior for you to fight.
Bottom line Infinite Undiscovery can remain fresh throughout. Star Ocean is getting really stale after a dozen hours. You are right about Infinite Undiscovery it does have far more replay then Star Ocean. Though I might also want to recommend Lost Odyssey if your looking for some good dialogue, story, and writing. I would recommend Blue Dragon for its very cerebral character building. So those are two ends of the spectrum for you to refine your taste from.







