Well, if nothing else she seems to have been pretty effective at uniting the Left...
Before my tie, so hard to say really. I've seen history programs that have made me wonder how politics even survived the power of the Unions. Surely it's worth thanking her for that. Democratically elected MPs should never have been cowed into submission time and again by unelected, undemocratic Unions as happened in the late 60s and 70s. Maybe the balance has slipped too much the other way, but from what I can see it was vital for a politician to take the Unions on and win for a change.
Failures are many, though perhaps she's guilty of failing to understand fully the consequences of some of her reforms, particularly all the privatisation and London's Stock Exchange Big Bang. In the long run that led indirectly to the current mess we are in though by no means is she the only one at fault for that - there were 11 years for Labour to fix it, after all.