Like all breeds of dog, there are variations.
In the same way, not all children get on with dogs. 
Broadly though, most greyhounds are gentle, laid back dogs. They don't need huge amounts of exercise, though will enjoy it if you provide it. If you want a dog that will do a 20 mile run and still have energy, they are not the dog for you. I'd also say they are not particularly bright but have certain specialised skills, including farting, counter surfing, sofa hogging, bed stealing and squirrel spotting.
Some find the loud hurly burly of very noisy family environments a bit much. Lots on here live very happily in family environments but this is something to bear in mind. For instance, ours hate it if we shout - not that we did much anyway, but now it means if we need to argue we do it very quietly, which is probably a good thing. 
Definitely pay a visit to the Pointy thread. Lots of rescue charities also run meet and greets, or greyhound walks so you can go along, meet a few hounds and ask lots of questions without any obligation. If you want to say where roughly in the UK you are, we can point (gedddit!!) you at the right charity.
Good luck!
By the way, they are completely addictive - one is never enough.