What is most important in a distortion unit?

[playon]

For me personally:

Sounds produced:

Should sound good at all gain settings, should allow some of the character of the guitar to come through even at high gain settings.
Plenty of output -- I like having the option of using the pedal as an overdrive, some pedals at lower gain settings do not have enough volume on tap.

Ease of use:

I don't care for more than four knobs at the most, preferably three.

[MohiZ]

Here are my entries:

(0. Price - I can't afford any boutique pedals)
1. Sounds produced
    Of course, the reason why I buy or make an effect, I want it to sound cool.
2. Versatility
    I don't want a pedal I can only use on one track. I want it to be able to produce different sounds and not just one. The more adjustments the better.
3. Ease of use
    This is a compromise with point 2. Sometimes an effect has many knobs that could be condensed into a single knob, or some settings are just not useful and should be fixed and not adjustable. Sometimes - mostly talking about distortion boxes now - some of the knobs really don't alter the sound too much and could be left fixed since they do not add to the versatility.

[slacker]

Make me sound like Bob Mould, if it glows in the dark then all the better

[WGTP]

It should make you "feel" like you are master of the universe, clear up skin blemishes (zits), your hair is ... the way you would like it to be, have a monster tool, all beautiful women want you, you have 10M in the bank, drive a Ferarri, make your 5 watt practice amp sound like a 100 watt raging mashall stack, etc, etc, and can play like (fill in the blank). 

It should meet your definition of sounding great, whatever that is, and inspire you to write and play the stuff legends are made of, look really cool and cost $39.00.

[Nasse]

I have said this, but I say it again. One thing we new guitar playing boys dreamed of was a secret device that blurs your sound cleverly so no one can hear your mistakes

[ayayay!]

For me personally:

Sounds produced:

Should sound good at all gain settings, should allow some of the character of the guitar to come through even at high gain settings.
Plenty of output -- I like having the option of using the pedal as an overdrive, some pedals at lower gain settings do not have enough volume on tap.

Ease of use:

I don't care for more than four knobs at the most, preferably three.

...yeah, that.  Basically.

R.G. is, sad but true, dead on.  I know we purists tend to think that our awesome pedals have the ability to sell themselves, and rightfully so.  But the truth is the slicker looking it is, the more it's gonna sell, assuming you've got a good sales team. 

I mean, there ARE more intuitive and easier to operate keyboards out there, but we've all been sold on QWERTY, so...

One thing I've gotta put my .02 in though.  Have you noticed out of distortion boxes we all want clarity, and out of boosters we want the option of a little bit of dirt?  Heh.