Ichigo's biggest personality trait is having no personality.
......
What the fuck?
Do you have any idea how dumb that sounds? The Soul King has no personality, because it's implied that he isn't even alive or even a *person*.
Let's put it another way, if Ichigo existed in real life and does what he does (i.e protective of his friends, really mature, looks on the bright side every once in awhile, loves his mother to death, and has a female best friend where they banter and get silly) would you seriously sit there and say "Hey dude, you have like, no personality, bro!"
Just because it's a personality you don't LIKE, doesn't mean it isn't there. There's an enormous fucking difference.