I think she looks lovely - it's not one of her top ten looks for me, however I've not really liked most of her state dinner / super formal attire. These occasions require proper gowns not just evening dresses and they can't be flashy in the celebrity sense.
All the more modern stuff she wears - the gold dress, those really sparkly Jenny Packham dresses she wears to premieres, high profile weddings and overseas cocktail engagements.
So I think she's stuck in a weird limbo for her age - has to be something formal, not too showy, work with the sashes for the medals etc, not clash with the Queen, not clash with the senior foreign female, be dignified, be the right designer for the occasion etc - I really disliked an odd blue creased gown she wore for one state dinner and another odd white fluffy one.
I agree with a PP that she needs to lop a good ten inches off the hair, but I understand wanting to hang onto the style of your youth for as long as possible too.