Personally, I think people are comparing the two FMAs way too early. BONES clearly wants to get all the arcs covered in the previous series out of the way as soon as possible. I attribute the light-hearted feel of the current series to this.

Will they continue the less serious approach all the way til the end? I can't say, but even then its not a bad thing. God only knows there are too many constipated heroes out there. Never learn to relax on the pot.