The best defense is offence heh. But i find oracle opening too weak against stationary defenses. If enemy scouted/spotted your oracle, he can rush forge and secure his workers. Or just leave 3 stalkers at base and proceed pushing/containing you.
At start of HotS i've seen a lot of oracle openings and i haven't lost to any of it. Probably because of me being too paranoid about what enemy is going to do and throwing Cannons everywhere.
I don't like the idea of attacking 4 gate protoss, because he will always have more units than you (if you are not 4-gating). At the point when he attacks me, i can retaliate him and push forward with immortals in attempt to destroy pylons that powers up his gates, right after it i throw nexus, retreat, wait for more units, and finish him off because i am way ahead in tech than he. us