We had one which we went to four times over the course of the year. The first time was fab, it'd only been open a week and was quite quiet, everything was new and clean, they even had a new coffee machine which made really lovely coffee.
Second visit, a few bits were broken, and some of the nicer staff seemed to be absent; third time, I found a dirty nappy in the ballpit. The staff removed it but left the area open and made no attempt to clean the balls (how do you clean balls in a ballpit?)
Was dragged there a fourth time by reluctant friends, more stuff broken, everything dirty, coffee machine replaced by instant and not even a proper boiling water but 'not quite hot enough to make tea' type urn affair.
DD picked up various colds etc. from the snot soaked masses (and no low basins for kids to wash hands before eating.)
However it was an interesting experience because, being the friendly soul I am I got talking to some of the mums, one had all five kids there because ('shhh they have chickenpox but they are almost over it now and everyone gets it anyway but the school won't 'ave 'em). Plus one mum who said she came every day since her son was excluded from school for fighting .
Which is not to say all people who go there are scumbags, but there are a fair few were I go that are a few short hops away from pond life.
I have been to other places. One was very nice, but very, very cliquey (it was a bit like Mumsnet ). The council run one is nice but always full of kids with green snotstreams (am I the only one who keeps the kids home when they have an obviously infectious disease?) And they won't let mums bounce on the bouncy castle, lest we bounce too hards and someone falls over. Kids are not allowed to bounce either, but if you look as if you are likely to jump they run after you with a big whistle and tell you off.