The whole charm of the series is the contrast of the "serious" main story and the silly sub-stories, so I guess if you dont like that, it's really not for you. Every game has heartwrenching moments, but I wouldnt blanket them as mature.

Dont generalize the whole series based on 7, its the only JRPG in the series for now, and if you dont like it just try 0. I love the series but 7 is my least favorite because its turn based.