I think it's fair to say she wasn't significantly worse than her contemporaries, even her lauded successor, Elizabeth I; it was a period where religion and politics were deeply intertwined, and warfare was constant across Europe. It's worth nothing that she killed fewer people over the course of her reign (283 is the exact number, I think) than her father did in single years of his, and her nickname and that of her sister were actually reversed in Ireland; instead of Bloody Mary, Irish Catholics were cursing Bloody Bess. English troops caused massive destruction in putting down Irish revolts, resulting in tens of thousands of deaths by starvation, in addition to the actual fighting.

Part of the reason we have the famous one-note perception of Mary is because her reign was ultimately quite short, so we only see the results of her immediate activities (suppressing Protestantism and losing Calais), rather than her long term policies (fiscal reform, naval expansion, and colonization), which bore fruit under Elizabeth. Her short reign was especially irksome with regards to Calais, since she was alive long enough to lose it upon entering war in support of her husband, Philip II, but not long enough to have a seat at the negotiating table at the end of the war, whereupon Spain and England passed out of personal union, and Philip had no problems letting the French keep Calais.