For a quick comparison:

1) Led UK to worst financial crisis in 100 years - £200 billion cost to the economy
2) Sold UK Gold reserves at an all time low - baking in a 'loss' of around £20 billion, double the cost of the ERM debacle
3) Signed Lisbon treaty in a cupboard with no referendum or acknowledgement
4) Enabled Tony Blair to ratchet up a high spend low tax economy
5) Plotted for years to become PM, only to lose election very badly when finally fought
6) Raised taxes spitefully on the day he left office to 50%
1) Plotted for years to become Prime Minster, only to very nearly lose and election she should have comfortably won against the worst ever opposition leader
2) Campaigned for Br, exit then led the most pathetic negotiation in history
3) Made political enemies even of her best friends like Damian Green
4) Did a deal with DUP to stay in Government that resulted in Government becoming impossible
5) Anti-Immigration stance throughout her career has impacted on culture of the Country
6) Completely lost control of Parliament resulting in no Governance at all
I wrote this out live, because I really thought she was awful, then recalled what Brown did and she has a long way to go yet. Not even on the same page as it happens. Still, hard to think of any other Prime Minister who has been less effective in the last 40 years other than Brown. Major looks competent by comparison.