Are the writings of Eusebius controversial?

I am reading "The History of the Church". I have thus far read a supposed letter from Christ himself written to an official, and a declaration that Christ descended into Hades following his Crucifixion (an idea which I think is accepted by some denominations, and rejected by others). Are these writings considered generally credible? I find it hard to believe that an actual letter from Christ would not be more well-known and revered, should it be accepted as legit.