I've had two b2b labours, neither what I'd call awful.
Both managed on Gas & Air, second in a birthing pool as well.
Ds1 at 36wks
Waters had broken a few days before, admitted to hospital, cx eventually started around 10pm. 3/4cm by 3am. 6cm by 6am, so taken down to labour ward.
Worth noting that I hadn't put much effort into learning my Hypnobirthing, and did my entire labour standing leaning on the bed with my elbows. Lying down for exams was not great, it was much easier standing. I had a great midwife, newly qualified and totally happy to let me do what o preferred.
Felt like an elephant was stood on my lower back, no pain in the front (that I noticed).
Ds1 turned just before delivery, kind boy! Standing delivery, three pushes over about 30 mins, born at 12:30pm. Active labour was recorded as 4hrs as it was 8cm to delivery.
2nd degree tear, two days of minor incontinence after but nothing major.
All in all, pretty good! Only 5lb5oz and a tiny head tho...
Ds2 at 38wks
Cx mildly at 9:30pm, un-ignorable by 2:30am, every 2-3mins by 3:30, arrived at birthing centre at 4am where they slowed to 4mins. Again, laboured standing, leaning on chair arms.
Had requested a pool, it took hours to fill due to a plumbing fault, got in at 6/7ish, and woooo that helped! Massively recommend it for b2b labours. It needs to be nice and hot, and beware the shivers if you have to get out for exams.
Ds2 did NOT turn for delivery (little bugger) and came out stargazing. He actually went back UP after one push, I remember saying "Oh come ON!" 
Took longer to crown as still b2b, tho the water helped with stinging, and I had my feet braced on the pool sides which also helped.
Delivered in the water at 9:30am, he came up very calm and not particularly squished. 6lb15oz, 2nd degree tear again, no urinary incontinence.
Again, tho a bit harder than Ds1's, still a good labour.
Felt brilliant after, home a day later, absolutely fine, full of beans.
However, I will say one less than positive thing, my pelvic floor is still lost 18m later, and I'm having physio to rebuild it.
My second midwife did say that she recommended I not have an epidural as in her experience of b2bs that generally lead to an instrumental birth, as the loss of feeling made it so much harder to birth a b2b baby. By the time I felt I couldn't cope on G&A it was too late for an epidural anyway!
B2B labours do suck, but they aren't all bad, and I feel certain both of mine were easier than many of my friends who had longer normal births.
All labours and births are different anyway, I hope this thread has helped dispel some fears.