It depends, one poor film doesn't make him a bad director, Cameron = Piranha 2 and Tim Burton = Dark Shadows.
It there is a continued streak, then yeah, maybe we can be worried but his other films have been good so far besides a film production is not simple, things go wrong, people interfere and so on, so its not always the fault of the director.
I'm guessing a few people around here may have had their faith shaken by Chappie's reviews.