Well, Alexandra was a really good mother, I am sure of that, but over-protective for sure. You can't blame her for that. After all I think it is quite normal with Alexei's illness and her fear for his life. Also she feared that her children would get 'corrupted' by the minds of Russian Nobbility. Alexandra's way of life after all was different from theirs.
As for Alexandra as Empress of Russia, she indeed did not like official receptions and so on but that was only due to her shyness and this prevented her for communicating pleasently with many people. Alexandra wanted to get to know people, and at Court people always would put masks on and be so formal that she must have felt uneasy about it. Yet one cannot say she was a bad Empress. She was not right for the official role in Court perhaps but she truly did care about the people whom she got to know in her role as Empress. This did show during the war when she became a nurse and got to know some of her patients, these men had often quite different ideas about the Empress and were amazed by how comforting and nice she really was. There is one thing that really got to me a while ago: Alexandra had a patient and the young man was sure to die. She kept him company and talked with him, comforted him and also she was heartbroken when the young man died. Also she and her family are said to have spent much of their fortunes on good works and war effort. This shows Alexandra as an Empress who really cared about the people, but who was strongly misunderstood, yet on political grounds she and Nicky both wanted to hold on to authocracy while many asked for a constitutional monarchy If they would have granted this, they would have been spared such a tragic fate, also she listened to much to Rasputin's advices on the replacement of Ministers and so on, this made her a weak ruler. Yet, she was a caring but misunderstood woman, and thus she was seen as the evil Empress while she was completely different.