Now this is something I've considered for a long time. And ultimately I don't think there is a finite answer, but here we go.

Technically Good Jazz
This would be your Tubby Hayes's and (early) John Coltrane's of the world. Every note is played. Their technical ability on their instruments shine through as they play nonuplets at 200bpm; while their harmonies and phrasing are perfectly precise. 

Unfortunately for these greats they leave many-a-jazz listener in the dust as they blaze a trail to the nth modulation of C#-7flat5 13. And there is a fine line between knowing what you're doing here, and doing what I call "Typewriter playing" (flying your fingers round the sax with little direction so fast that no-one can really hear what you're playing)

So hear we have immense skill, but only for those worthy enough to be able to hear it; many of the intricate and delicate harmonies being hidden away in hemi-demi-semi-quavers. I remember when I was younger I would listen to these guys and leave with a headache. But I kept going back, because every time I did a new harmony was un-earthed, a new level to their solo was unlocked.

I could listen to the same piece, Giant Steps for example, for 10 years straight and still find new things to enjoy and hear about it. I know this because I have!

Ethereal Jazz
Now this would be every band that lays down a dorian minor chord and plays vertical solos relying on one or two sweet notes or blue tones.

The solos are long, as are the notes within. Often with overtones, large variations in pitch and often sticking to one night a playing it over and over.

There is nothing to miss here. And often I find there is nothing here. The pace is so slow I often find myself thinking "Are they really amazing and playing the subtlest of intervals...or are they just shit?" 

When this music is played right it provides you a window into the soloists soul. You really can feel their music and connect to the musician. This accessibility is largely why it is popular. 

This is the kind of music you would want to relax to, however. Something you'd smoke a pipe to, or perhaps some other shag. Whilst relaxing in a big chair; surveying the bustle of London. Like a big pretentious nob.

Now I think there are some real gems in this genre, and some absolutely fantastic musicians who can spin a whole story in just 3 notes (Think Miles Davis) but the nature of the beast allows far too many talentless pretenders to have a go, because at it's core this jazz is easy. 

Earning a Crust Jazz
This is the jazz all musicians hate to play. Its your straight blueses, your Autumn Leaves your long winded vocal numbers from 1920 and your Oh When The Saints!

But, this is the music that we all get asked to play. Ten times more often than any other type. 

We don't really mind playing this music, but jazz is about the pursuit of new sounds; new feelings, new rhythms, harmonies, intervals and melodies. So re-visiting the same tired 2-5-1's every week quickly becomes tiresome.

And the thing we hate the most about this music. Is that sometimes, we enjoy it. You'll find yourself singing along, tapping your foot and enjoying your wanky 12 bar blues solo comprised entirely from the pentatonic minor! Then after you will feel dirty, and ashamed. You see this kind of jazz is like a riding a mo-ped; great fun while you're on it, but you'd never want your friends to know about it.

Someone's experience of jazz is entirely subjective, this is why there will never be a definitive answer. I find the technical jazz exhilarating and exciting - others find it to be an exercise in mathematics and showing off how big your nob is.

Jazz comes down to a listeners experience. If they enjoy it, and get value from the music be it by a connection the the musician or music itself or by an intellectual gratification of the music or simply by hearing a tune you know and love; then it is good jazz!
I went to see some acclaimed LJF jazz at the green note last night. I remember excitedly telling the immediate company that "this was the band that played with ronnie scott" and "I've seen the pianist John Critchinson before with Simon Spillett" so you'll understand how shocked I was when the band started with what could only be described as a mix of minimal tech, trance and synth-jazz.

You see there is the Green Note, in Parkway. And the Green Man, on Euston Rd. The stalwart John Critchinson was at the Green Man...sadface.

After my initial reaction that I was listening to three wankers who didn't have a clue about music I realised there was some talent and skill in there. Mixed in with three and a half kilograms of pretentious noodling. I've always been of the opinion you have to get really good, before you can play really bad. Think 1960's John Coltrane i.e. post Giant Steps era.

There were a few good tunes in there, but there was little refinement and little technical skill. I must say their use of the loops and synths was an interesting addition and I could see it working.

Or to put it better, you would have to be really, really high to enjoy their music.

I was pleasantly surprised and relieved by the second band, headed up by pianist and composer Sam Leak, featuring tenor saxophonist James Allsopp.

Their music was truly beautiful to listen to. Heavy on modal and modulations mixed with an ethereal time feel and it all worked. Everything was tied together, even by the tiniest thread at times.

It was also obvious that these people lived their music. They were engaged with what they were playing, sometimes so much you could almost see the tears. 

A real pleasure to listen too!

If you haven't been to the Green Note before they run a jazz night on the first Sunday of every month which ends in a Jazz Jam. Well worth checking out.