Use the Pheonix to counter battlecruisers. Those direct AA are quite effective against large air. Corrupters for the zerg work well as well.
Science vessels were retarded against zerg in starcraft 1.... Build like 12 of them, have them all use irradiate on eachother, move over a zerg army... you insta gib everytyhing. Well, if they have tons of hydralisks you might need more, but.... Yeah, two irradiated vessels could easily spell doom to any of your expos unless you have several towers near there... and with the clumping tendancies of mutalisks, a single irratiate could wipe out a squad of 30 or more if you cant move the right one out of the way fast enough... which since they are often clumped due to that tendancy means your mutalisks are dead before you can do anything.
Science vessels were retarded against zerg in starcraft 1.... Build like 12 of them, have them all use irradiate on eachother, move over a zerg army... you insta gib everytyhing. Well, if they have tons of hydralisks you might need more, but.... Yeah, two irradiated vessels could easily spell doom to any of your expos unless you have several towers near there... and with the clumping tendancies of mutalisks, a single irratiate could wipe out a squad of 30 or more if you cant move the right one out of the way fast enough... which since they are often clumped due to that tendancy means your mutalisks are dead before you can do anything.