Completed all of the SO's barring 1, which is weird because it's not a series I hold in particularly high regard. I did find 2 to be the most overall enjoyable, but only in the sense that it was a competent JRPG, rather than it being particularly notable.

In regards to SO4, I did like that they were making an attempt to have the game actually be Sci-Fi throughout for once, rather than fantasy with sci-fi tacked on. However the game totally lost me when (SPOILER)Edge literally destroyed the Earth in the alternate dimension. Seriously something that drastic was handled so poorly by the story and then eventually forgotten. You don't blow up a freakin' planet and then shake it off like a bad cold!

Anyway, it's like most TriAce games; you tend to come for the combat rather than the story. If you don't find the combat engaging then you won't like the game. Personally I found SO4's combat to be a bit more interesting in terms of gameplay than SO3, which really came down to spamming certain moves in chains continuously (Side Kick! Side Kick! Side Kick! Side Kick! etc.). I don't know where the idea of their being less intricacies in SO4 compared to SO3 comes from. Is it in the item creation side? If so then I always found that to be one of the weaker aspect of the game, since it really just tended to pad out the game than add to it, and was an egregious example of guide dang it.