My eldest went to a very good one and I think the reasons it was good were...highly qualified mature staff (youngest was about 35) with their own children, only took children from 18 months, had keyworkers, had a maximum of about 30 children. I am not saying a nursery has to have all these things but I think having these things makes it more likely that care will be good.
I know 2 people who don't really like kids who went into childcare and one even faked their portfolio (ie. said they did a 6 month study which they didn't). I would not want these looking after my kids!!! I also hear them talking about they feel sorry for the 'little babies' in their care for 40 hours a week, this attitude seems fairly common from what i hear.
I think alot of nurseries are more about profit than care, like most things in our society. It's underpaid and undervalued. Probably, in part, as children and dependants don't make money so are not 'important' as with old people and stay home mums for example.
I didn't use nurseries with my last 4 DC and am glad i didn't have to. I think some kids can like them and some hate them. I think there is a danger to very young babies being there in excess of 40 hours a week. it just seems a shame to me, that is through doing it myself with DD1.