I know this will surprise no one bu I really care about having them as viable options in battle. And where OO has been generous and RK as well (I don't have all for them but they're both pretty solid) I HATE that you can't even use an unit if you don't get it in BE. and that to unlock the last level you NEED another 5* unit of the same type
FGO is....if you like Fate then it's a solid story in all of that, plus playing around with all the characters, but the gold drop rate is semi evil....but all the 1-3* servants are viable for story and events too with work
fgo gacha is worse but I've been thoroughly been enjoying the story, and FFDOO remains roughly balanced in its own weird ways