Overpowered against humans - while pro players use it. And i verify this.
Those times i use Adv. Marauder, as bit in-between of above average/rookie player, it does considerable damage to tightly built bases. And died many times when properly built (i. e. turrets covering buildings while far enough from nodes and stuff to zap.)
Spreaded bases manage to get maras quite well, and if pro, they only inflikt heavy damage minus 1-2 turrets. With someone guarding or group of campers
So... devastating in hands of pro, great annoyance for those who knew to use adv. mara, but not enough skills, and only slight nuisance for untrained or someone who's unknown of mara's powers.
Like Conzul said:
Aliens have always had to build carefully. Now, humans must as well. Acclimate!
Any more? Pretty much same above the others.