I visited Nyamata Genocide Memorial and Kigali Genocide Memorial in 2015.  

Kigali Genocide Memorial is more of a museum than a "site".  The Memorial Centre illustrates the unsanitized horrors of the genocide while being very respectful to the victims.  Similarly, despite being a place borne out of profoundness sadness, the Centre also manages to express the optimism of the Rwandan people.

Nyamata is a quiet rural town, which can be visited as a day trip from Kigali.  The now UNESCO designated site did not have a site guide when my friend and I visited.  Indeed, the two of us were the only visitors.  Inside the church were bloodied clothing of the victims.  Similar to the other reviewer on this site, I did not feel comfortable taking photos inside the church. 

To understand the anger-inducing callousness and failure of the outside world to prevent or reduce the human suffering that occurred in Rwanda, I recommend "Shake Hands with the Devil: The Failure of Humanity in Rwanda" by former Lieutenant-General Roméo Dallaire of the Canadian Forces.