Plasma weapons have always been very useful. They have their uses just like human weapons. Human weapons aren't very good at taking down shields, but they are health. Plasma weapons aren't good at taking down health but tear through shields.
I always hated when in COD I would join into a game in it's last 30 seconds just to be on the loosing team. It happens every other game and I was really upset when I found out this was in H4.