it ain't bad
I play a PC with the intimidating rage feat. I have to admit I would not have taken it except for the fact you have to have it to play be a Frenzied Berserker.
As someone pointed out the first thing one must keep in mind is to remember to use it.

I'm always forgetting I can do it because you are only able to during a rage.
When I have remembered to use it, it has come in very handy. My PC has a low charisma but even so I can usually force at least one opponent to become shaken every fight.
I will have to say that my DM kinda house-ruled the feat for me a bit. He ruled that if I succeed in causing someone to be shaken that if I can make them fail a second or even a third save vs. my intimidating rage that their fear increases which causes them to go into the deeper stages of fear.
Basically if I keep focusing my intimidating rage on the same opponent and they keep failing I can take them from shaken, to frightened, to panicked in just three rounds.
Hasn't happened yet, the best I've gotten is one guy failed twice and became firghtened, but I am hopeful that one day it will.