I have a lot of experience with hypnotherapy and have come to the following conclusion for myself.
It works under the right circumstaces - the therapist needs to be good, and you need to trust said person and be open to their suggestions.
Practical example of this:
I have a phobia of being injected, blood taken, stictches... needly things, but not the needle in itself. No - not a fear, but an actual phobia, with unconciousness and involuntary convulsions being the end result.
* About 16 years ago my surfboard flew into my face, gashing my open from eye to cheek, meaning that I needed stitches. The doctor said that I could lose my eye if infection sets in, and I have no choice but to get stitched.
I explained to him my situation and that stitching me will be "impossible"and that I've tried to get over my phobia when my parents sent me to a Hypnotherapis before, who didn't really achieve anything. It so happens that the doc knew my previous therapist (i dont come from a big city) and he mentioned that he's done a similar course, though his methods are more agressive.
Long story short, I agreed to be stitched - thinking that the doc will "calm me down" using hypnosis and then when I've settled, proceed to stitch me. I recall him taking me through "the steps" and putting me in my "safe calm place" and felt him cleaning my face off. When he brought me back up again, I told him that he can go ahead and sew me up. One of the happiest moment in my life followed, when he told me that he'd completed the stitching while I was under.
In this scenario, hypnosis was like a miracle to me, however I have a contradicting anecdote as well.
Fast forward 14 years and I'm back at the same doctor, hoping he can help me mentally prepare for a medical procedure, for which I will need to be sedated for. (catch 22 situation - being sedated because of my phobia, but the only way to sedate me is by putting a needle in my hand). I havent seen this doc in that time, but when I saw him, I didn't recognise him and thought to myself that he doesn;t look like the man I was in awe of when I was a 16 year old kid. I thought he looked like a weedy nerdy type in fact. I went ahead with the therapy regardless and during the time I was in my safe place again, he put a needle in my hand to simulate the sedation needle. This lead to the worst and nigh on instantanious convulsions I've ever had. When I woke up from the attack, I was drenched in sweat like I had jumped into a swimming pool fully clothed.
So I guess all of the above is "cool story bro", but as I said, it's lead me to the conclusion that it does work, but depends entirely on you and your perception of the person administering the therapy and their skill as a therapist.
For what it's worth, through the years I've actually gotten better, and I put it dopwn to seing hypnotherapists sporadically through my life.