I was at its first incarnation, in Covent Garden in 1975*. I worked as a volunteer at Ally Pally, slept on the stage, built scaffolding, drank lambik for the first time, met some wonderful people.
It's a cumbersome, crowded, noisy event with too few seats, inadequate toilets and an arbitrary selection of beers. Imperfect. But a celebration. A celebration of beer.
Hundreds of beers from all over the world. Prices are lower than most pubs. Huge numbers of the general public. Organised and staffed by volunteers (which is why the prices are so low). US cask beers** you never see in Europe.
Yeah, rubbish festival.
Don't whinge about what it isn't. Celebrate the GBBF for what it is.
* With Martin Young. The second time I visited London.
** US brewers seem to have no problem sending cask to the GBBF.