Basically, if you're spamming cure and overhealing by 200% you'll get the job done but you're not 'good', per se. If you're standing around for several cooldowns at a time waiting for healing to matter, you're inconsiderate. If you let someone die because you made a mistake (forgot a tankbuster was incoming, ran out of oGCDs, generally not paying attention) then that's forgivable. If you're consistently letting people die, you're a bad healer. If you are pulling people's ass out of the frying pan in a fight that isn't going well or you're keeping people alive while pumping out at least SOME damage then you're golden.