http://www.bbcattery.co.uk/page3.html

This cattery is similar to where I work though a bit bigger by the looks.

My job is in a cattery this boards cats. No dogs, we also board guinea pigs and rabbits but they are in a seperate place. I'd try to find one that isn't next to dogs or if it's both they should be apart from eachother not close together.

Most importantly cats need to be vaccinated and have their certificates with them so the cattery owner can keep them. This is to ensure that there is no spread of infection.
Between each pen in the cattery where I work they have perspex up to half way so this acts as a sneeze guard (also to stop the spread of infections)

Each pen can house up to two cats, there are two pens for a family of up to five cats. There shouldn't be overcrowding.

It should be very clean, with clean litter trays every day, with fresh water every day also.
Where I work they have a nice big bark tree stump to climb on and scratch claws which takes them up to a small wooden seat so they can sit and look out or have a snooze.
They have a step up to their little house which is secure and they can hide and sleep here if they want to stay inside. Their bed and food are in there, they have a heated mat and fleece to lay on here too. With carpets put in for comfort. (These are taken out and cleaned after each cat)
They have the radio on, I turn it to classical after I've cleaned the pen so they can relax, and I've noticed that the cats find it calming.
Where I work it's based on farm land so there are chickens going back and forth and ducks, and also outside cats for them to watch if they want.
They have a selection of mice and toys to play with if they want.
Brushing is done if it's asked for, some charge extra for this. And we also administer medication of needed.

So basically there are few things that are a given when looking at a cattery (boarding)

Clean, airy and open environment
Beds and blankets
Safe secure sleeping quarters within the pen.
Space to walk around in to stretch
A seat or somewhere they can sit and watch or sleep
Fresh water
Clean litter tray
Some kind of stimulation like a radio or TV that they can hear or see
Toys so they can have a play should they want to

I find that the cats in my workplace are always very happy, you get the odd hyperactive ones that demand more attention, but most are happy to while away the hours on their heated mat (even in the summer!) and snooze the day away.

I think the main thing to think is 'if I were a cat does this have everything I want and need?'
If it does then it'd probably be okay.