Oh man it's been years and years and years
I don't recall any mission having an objective outside of 'kill all enemies' or 'kill the boss'. I have a hard time even classifying it as a SRPG as there little to not strategy to be found. The enemies just don't push back enough to be a real threat.
BUT it's enjoyable as a fanservice vehicle, the crossovers and roster is just a lot of fun. I would be hard pressed to call the turn-by-turn combat anything more than clearing an endless stream of trash mobs. As someone who plays his share of fighting games and is no stranger to spending time in the training room, punching what is essentially an army of training dummies in more flashy and optimal ways didn't bother me, but your mileage may vary. You may find yourself burned out before you complete the series.