For me (my opinion only, as always) she is the epitomy of a monarch, she's class personified, she has a great sense of humor and also has the best "we are not amused" face in the world (yes, in the whole world, from Debrecen to Alaska
) when she doesn't like something.
As far as "what has she achieved" i'm getting a bit of a deja vu from the TRF thread "Achievements of Diana, princess of Wales", but for me to name a few things that she did that may have changed things for at least one person in the world: she was one of the first (the first?) royal to visit a leper colony, i think she is a Symbol for many of the Commonwealth countries, she spoke irish on her visit to Ireland, and touched many individual lives
Imo P.Philip is a big support to her, but different than Q.Victoria I've always felt QEII was the true monarch and not steered by her husband; but will leave it at that for comparisons with other monarchs, because as you might have guessed from above, any other comparisons will always have her come out on top
And as i am mainly interested in royalty because of the history of it, i also appreciate that she is both a traditional successor of her father, grandfather etc, but still managed to slowly modernize the archaic monarchy in one which at least will have a chance to continue after her; if she hadn't done that, i think things would start to fall apart real soon...
Oh, and i love her "helicopter entrance" at the 2012 olympics
okay, i'm done now