Having too happy sims were one of the things that made go looking for mods way back when. I had a sim who was angry from an incident at work, he came home and was instantly happy. Then there was a long time when I had no decorations at all, my sims were living in bare boxes just so that I would be able to see them being bored, sad or just plain fine. Then I began to mod my game "Shimrod's Happy Buffs Changed To Fine". Now I use roBurky's meaningful stories mod, so no happy moodlet's for me. Or unhappy either.
I guess they are trying to do something about the sims being constantly happy indoors earlier.