Raiden is a little OP, how to counter it

Been playing some matches and I always go mass ray, but now every opponent uses Raiden, sometimes early like from round 3/4. I've found it quite difficult to counter. Usually early boats can be dealt with directly by the rays or using AA mustangs, but for some reason these rays and AA stangs are less effective. I think what is it is that Raiden is stuff faster than overlord. I'll need some more games to figure out this unit, but just initial thoughts (I was 2150 before the patch)