I personally think terran is overpowered, but only if you know how to use them. Think about it, Science vessels can use EMP shockwave against protoss units. Ghosts can lock down protoss and terran units. Terran has a balanced resource cost and unit power. The buildings can fly. The buildings can be repaired faster than any other races buildings. Medics can heal any units than an SCV can't repair. There are turrets for anti air and bunkers for anti air/ground. Battlecruisers have Yamato cannon, the highest amount of life of any unit. Siege tanks can shoot while they are moving, and they have the highest range of any unit in the game. Only bad thing is that SCV's will usually lose against drones or probes.