I did Henna once. Just once.
The color was great.
The smell and texture was awful.
I've been told it would have been better with practice, but the time and production going into it just didn't suit me.
Texture got better after a few washings and rinsing out some leave in conditioner (if I remember right)

I love henna, and have been using it for years. It is messy and smelly, and if you are doing it for the first couple times, I recommend having a friend help you (prefferably someone with dying experiance) and I like to put cinnamon and ginger in the mix to bring out the blonde and make it smell better. One thing you have to be really careful with is that if you have ANY other type of dye in your hair, it needs to be totally stripped out, or your hair will turn green (henna doesn't mix with anything else but henna). Henna is considered to be semi-permanent and will not rinse out, but I love what it does to the texture of my hair, and it looks really natural as it grows out (no one who doesn't know henna can tell that I dye my hair usually).

If you have long healthy hair
DON'T DO IT!!!
I had hair to my but and it frizzled and dried it.
Also things labeled Organic Henna aren't because of importing laws and labling rules...or lack there of. Even Rainbow from my local trusted herb store was the poison and not the real thing.
Be aware that any mix with 'real' henna will permanently color your hair reddish, even after the walnut or indigo washes away. I am still growing mine out.
It is stiffer and breaks more easily, and tangles more easily.
Please before trying anything read everything on this website
www.hennapage.com/
including warnings.
Be aware that even though this woman is good at her craft, Indigo mixed with lemon (browns, and blacks) is kinda toxic
And gave me a constant bad headache for a week.
I just wouldn't ever, ever do it again.