Depends on the type of holiday and definitely depends on the type of child/ren you have.
Mine are on the go constantly, they are nightmares for sleeping and napping anyway so on holiday it is magnified. Someone posted about naps and afternoon beers - my kids don't sleep when they are in an exciting/new/different place. We were/are walking them in the buggy at 12-1am every night with them still chattering away/screaming to get out, just the sound of a car will wake them up etc.
They also don't eat anything, so restaurants are difficult which means self catering, which means me shopping and cooking in different places for food they will eat. If we do go to a restaurant they wont sit in a high chair, lob food around and screech. We take it in turns to bolt our food and chase the children as they leg it or accost innocent holiday makers trying to enjoy a quiet meal.
Constant danger - nothing child proofed which means absolutely no chance of sitting down and relaxing for a second. Balcony/terrace doors always locked so sweltering heat. On the beach they just plummet straight into the water, or run into the road, or (my personal favourite) stamp on all the other children's sand castles, or splash strangers with water/sand etc. After 2 hours we are exhausted from chasing and carrying heavy screaming children away and apologising. (they on the other hand are not exhausted at all).
No toys. No internet. No tv. No entertainment. Which equals boredom and destruction.
Very tiring and not much of a holiday.
Center parcs was fine but felt like no kind of holiday i would really want to go on. I can spend hours in our local pool and cook at home if i want that kind of experience.
We are doing Eurocamp in July but i'm not optimistic. I don't mind the holidays being shit, i just mind them being shit and costing a fortune. I came back from Majorca last year and cried at spending 3k on 10 days of hell.
It's all just groundhog day in a worse location with less help.