I visited this WHS in July 2019 and spent 5 nights here; 3 based near Ulswater and 2 based near Keswick. To try to cover as much ground as possible I did a combination of driving through nerve-wrecking narrow country roads as well as a number of different hikes.
Even though it is a cultural landscape WHS, the Lake District could easily have been a mixed site. There aren't very remarkable historic sites around Lake District National Park although I must say I really enjoyed the Stone Circle of Castlerigg, Wray Castle and what's left of Pullney Bridge which was hard hit by the 2015 floods.
My favourite lakes were those of Ulswater (photo) and Wastwater. Apart from the very pleasant easy walks of Friar's Crag and Centenary Stone, my favourite hike at Ulswater was the uphill hike around Gowbarrow Fell, past the touristy Aira Force Cascades.
My favourite driving experiences and stopover points were at Honister Pass (with short hikes to lovely waterfalls) and at Kirkston Pass with a number of mandatory stopovers at the Kirkston Pass Inn, one of the highest pubs in the UK. At Buttermere, make sure to stop by the Syke Farm Tea Room for great ice creams. Of all the lakes, Windermere was by far the most busy and the least interesting and 'outstanding' in my opinion. Nonetheless, the Claife Viewing Station and Courtyard are a good spot for a panoramic photo.
Tarn Hows and Black Crag were another highlight of the Lake District NP providing excellent views over Langdale and the Coniston Fells. Apart from the loop around the tarn, I also tried out the Tom Gill cascades hike even though the best time to visit is probably in autumn for the colourful foliage season. There were almost no signs of wildlife or birds when I visited even though the red squirrels seem to be making a slow comeback.
To make up for this, as a bird watcher I went to the Esthwaite Water Site of Special Scientific Interest (SSSI) which is situated between Windermere and Coniston Water. Esthwaite is a mesotrophic lake but what brought me here was a pair of osprey that built their nest in the middle of the lake on a treetop. From the cafeteria near the lake, a webcam placed above the nest provided a very good livestream of the 2 adult ospreys and their two juvenile offspring. I also hired a self-drive boat to go closer to the nest and used my binoculars and zoom lens to watch the birds without disturbing them too much.
All in all this idyllic and scenic WHS was very pleasant to visit and I felt it possesses OUV. Even though it isn't one of the top WHS on the list, it definitely is one of the UK's most visited and rightly so. As a tip, avoid renting bigger cars to visit the Lake District as the roads are really narrow at times.