Good things: response to Falklands crisis, strengthened UK's position in Europe, curtailed worst abuses by trade unions, supported perestroika.
Bad things: introduced poll tax (most regressive form of tax imaginable), removed workers' rights, massively increased income disparity, massively reduced industrial capacity, slashed investment in schools, health care and infrastructure, put millions out of work (ok, maybe not all her fault), allowed countless communities to go to the wall because they weren't "one-of-us" and therefore, to her mind, worthless.
Oh, yeah, the milk thing too.