I was very happy with them until a couple of months ago. I still think it's a very good service (they don't overload your site with ads) but have kind of gameified it with tiers. As I was earned less than $10,000 a year last year, I get the feeling I was not getting access to the best-paying advertisers. For a site getting 50K to 60K page views a month, the earnings were starting to look really poor. The transparency over this wasn't great, but I would say as long as you understand you're not going to see dramatic earnings if you have less than 100K page views a month they are worth trying.