I've only done one audax (200km) but I hated:-
1) At the penultimate control, the Coop store in Wheelock, I had the following conversation with the cashier as I bought the obligatory flap jack/milk shake/can of cola/Ginster's/etc
Him: "Lots of cyclists in here today."
Me: "Yes, there's a bike event on. When were the last ones here ?"
Him; "About two hours ago."
2) An hour later, in the pouring rain, wondering if I'd missed a turn in the (pitch) dark. Did I suggest to the demoralised GF that a) we stop and go back a few miles to check or b) we press on and hope ? We did b) and it turned out to be the correct answer.
3) At the last control, the Shell garage at Dean Row next to the Unicorn pub, the till crashed and it took 15 minutes before it would reboot and give me two receipts for two packs of Kettle Chips. Demoralised GF (outside looking after the bikes) was really losing the will to live.
4) Getting back to the car in the formerly packed layby, to find that mine was the only one there. I started the engine, turned the heater and seats on full and put the DM GF in the car while I hung the bikes on the carrier.
Despite DM GF's experience, we did a 300km ride the following month and DD a few weeks after that.
I'd have gone on to do more audax last year if I hadn't had my bike nicked in January and I fully intend to start this year.
I've ordered an England Audax shirt, how can I not ?