This is essentially my view too. Mulholland Drive and Blue Velvet are the beginning to end masterpieces. The first few episodes of series one of Twin Peaks are even better but then tail off hard. The rest is a bit of a mixture really. Lost Highway, despite being so so, has the second greatest film depiction of oily white boy saxophone in American cinema (the greatest is of course Tim Capello in Lost Boys) and had a soundtrack that radicalised a generation, myself included.
But overall he achieved one of the greatest things that I think an artist can, which is to re-invent the world, such that it is different for having him in it, and people recognise it differently.