Ultras aren't really that great. Even when fast Ultras, because they just take too long. They make good damage sponges, but they are TOO expensive.
Queens are excellent units. Ensare is a good ability, parasite can be fun, and helpful. Spawn broodling is also good, epsecially against a group of tanks. Just make a broodling out of the tank in the front, and all the others will attack it and probably end up blowing themselves up.
As far as the zerg missions in BW . . . try going muta/guard. I can't help you much there . . . I never was much for good strats against the computer.
. . . The one thing to remember about the computer is: once you find a strat that works on it, keep using it. Also, it generally always has a pattern that it follows . . . if you can figure that out, you're in good shape.
Try to micro against it. Maybe get fast hydras and spread them out for the carriers, unless the comp has lots of zealots.
Once you get rid of most of it's air, just fly mutes around it's base. Attack in short bursts and then fly off to another target, to evade its dragoons.
Like I said, I don't know how good this works . . . the comp can be a b*tch sometimes in those single player missions.