I have a fair amount of sympathy for Mary I. I abhor her persecution of the Protestants, but we have to remember that such behaviour was in the blood. Her granny Isabella wasn't very kindly when it came to those she considered heretics either.
I think the reason I sympathise with her is the thought of how much disappointment and uncertainty she suffered in her life. She went from being the Jewel of England, the only heir, to being a bastard, forced to serve her infant half-sister. THEN she had to live under the rule of her fanatical Protestant younger brother, this of course, after living in fear for her life both proir to and after the death of her mother. After this came the travesty that was Queen Jane, and then FINALLY she succeeds to her rightful place, the position of power she was born to. Most likely she expected that all would be well, that she would produce an heir and continue setting England 'to rights'. Imagine what it must have been like for this lady to not only deal with the humiliation and heartbreak of two phantom pregnancies (or whatever phenomenon they were), only to realise that the husband she had fallen in love with against all expectations, had abandoned her and was paying court to her younger half-sister!!
Not to mention how atrocious it must have been for her to realise that so many of her subjects wished to see Anne Boleyn's daughter on the throne!!!