I've started it twice and finished it once.
In my first year I got taken down by a chaingang of cretins who overtook on a sharp left corner and pulled in sharply to avoid an oncoming car. One of them put his pedal into the spokes of my front wheel and broke about 10 of them. So I had a long walk in the rain to the nearest village, an expensive cab journey at 2am to the nearest railway station, and a freezing wait for the first time home. Definitely type 2 fun.
The second year, however, was brilliant. A warm, dry evening with a clear sky, a full moon and a slight tailwind. Riding through open fields with only the moon lighting the road in front of you is amazing, and although both times were busy, I'm going to do it again this year.
Like a sportive, avoid the Strava-chasing chain-gangs of muppets with no actual experience of riding in a pack and you'll probably be fine.
And expect very long queues at the cafe at the end if you arrive after dawn!