This is the only WHS that I have been to multiple times, due to living in California, and it truly is a highlight of not only CA but the USA as a whole. It is a beautiful and unique landscape that rewards multiple visits. I have only been in summer because that is when most trails are open for hiking, but I have heard that it is gorgeous in all seasons. I actually would not recommend a visit in high summer due to crowds and the reservation system that they have put in place. The Valley can become a circus very quickly, especially in the summer season. I would recommend a visit in fall.

I have done the hike up to Yosemite falls, and while it is amazing when you make it to the top, the trail itself is basically an endless staircase that is usually pretty crowded. We actually underestimated the amount of water that we needed as well, which led to an eventual race down to the bottom so we could get extra water from the car. So please don't underestimate this hike in particular, it is brutal! (The falls are very nice from the bottom as well).

You can hike to the top of Half Dome as well, but that requires a special permit that is awarded in a lottery system, as well as an absence of a fear of heights. 

There are other areas of the park that are nice and free of crowds. Hetch Hetchy and Tuolumne Meadows have hiking trails and are undervisited compared to the valley. These areas deserve love too!