TL;DR: the foundation is apparently fairly closed. The reason for skepticism is that they spend a lot of money without a public decision making process. They spend more money than many countries on healthcare and if they decide to pull the plug on certain projects, those projects are going to have a very tough time.<p>I personally don't really see a need to worry or be skeptical. They've been doing this for over a decade and so far it's going great. I'd be grateful rather than skeptical about them spending so much money on projects that otherwise could not exist the way they do.
They have certainly made mistakes in the past (health clinics move people 50 miles to receive treatment for AIDS and send them back to die for diarrhea because their focus is too narrow).<p>The question I'm interested in is if they have improved and learned.<p>The problem is that there is not enough information for outsiders to analyze them and scrutinize the result. Gates may spend his money inefficiently because he can't get the data he needs. They should use open data and be open to criticism to improve.