I think the suggested names are all quite interesting - because we all tend to concentrate on failings of character rather than anything else - and failings of character don't always make a bad monarch.
Not many of the ones mentioned would make my top ten - for what its worth here's a few of my top ten - i've only chosen Royal figures who actually exercised power or who had a significant influence on poltical events..
1) Mary Stuart - more sinned against than sinning perhaps, but a woman who put her own desires above those of her nation, despite a childhood dominated by her uncles and her french in laws did little after returning to Scotland to prove she could be a capable monarch, her death might lie at English hands but the English didn't depose her, completely undeserving of her "martyr" status, a status she actively sought after her trial and condemnation.
2) Edward VIII (Duke of Windsor) - and not because he married Mrs Simpson (who i believe was the real victim of the abdication), rather spoilt and difficult individual, who had little concept of duty or responsibility, who's rare good deeds were thrown away by his many attempts to steal the spotlight after his abdication, his consistant failure to appreciate the limitations of a constitutional or parliamentary monarchy, for me the one thing that shows his general shallowness is the comment at dinner after visiting poverty stricken Wales (the visit that has prompted many to suggest an establishment conspiracy to get rid of him) telling people he approved of "splendour" - the same day he ordered yet another trinket from Cartier for Wallis - i am sorry his many apologists haven't quite sold him to me.
3) Richard III - again despite his apologist his actions lead to the collapse of his family and dynasty - whatever we think his nephews vanished from view during his reign, his actions in the months following his brothers death - don't suggest a man who wasn't willing to usurp his nephew's throne and his relationships with his brother's wife seem to have been amicable until Edward IV's death so those actions shouldn't be considered an attempt to protect himself from her and her relations whose greed has also tended to be rather exagerated.
4) Alexandra Feodorovna of Russia (consort of Nicholas II) - whilst anyone would sympathise with her for her difficulties and the position she found herself in and particularly her son's illness - she was a rather foolish, selfish woman who made in my opinion a significant contribution to the collapse of Imperial Russia.
Just a few of mine rather than 10 which seems a high number to me!
