Firstly, two days (minimum) in the park is highly recommended. Anyone who complains the park is too full of tourists likely only visited the park for one day (on a weekend) and spent most of their time in Yosemite Valley during the afternoon, which does get fairly busy. Once you get to the northern section of the park the amount of vehicles slowly dwindles and you are once again in wilderness.
My wife and I had whole lakes, meadows, and forests to ourselves (especially if you get going early). We layed out a light picnic alongside Tenaya lake which reflected the majestic mountains. Its difficult to describe how amazing Yosemite really is. Treat yourself and enjoy the whole park in more than one day. Between 2009 - 2023 I've made 5 trips to the park, including camping inside the park (make reservations early).
Highlights:
Glacier Point Road - Sentinel Dome Hike (1hr) & Taft Point Hike (1hr)
Sequoia Groves - Mariposa & Tuolumne (note that the most impressive Sequoia's are found in the Giant Forest Grove in Sequoia National Park)
Tioga Road - Tuolumne Meadows, Lukens Lake, Tenaya Lake
Hetch Hetchy - Hike to Tueeulala and Wapama Falls (2-3 hrs)
Historic Yosemite Parkitecture (5 National Historic Landmarks) - Le Conte Memorial Lodge, Ranger's Club, The Ahwahnee, Wawona Hotel, and Parsons Memorial Lodge
Yosemite Valley: Late Spring/Early Summer is peak season (plan accordingly), the waterfalls in Yosemite Valley and Hetch Hetchy are in full glory (the latter with far fewer visitors). Many of these visitors only go to Yosemite Valley. I would recommend many visitors to consider an off-season visit to the park. If visiting during peak season, start early and if possible plan on a weekday visit to Yosemite Valley. Yosemite Valley is beautiful, but I would argue the top of the valley is just as spectacular as the bottom. Taft Point and Sentinel Dome located on Glacier Point are incredible. I've previously highlighted the cultural value of Yosemite Valley, it's influential and checkered conservation history even predates Yellowstone.
Hetch Hetchy Valley/Reservoir: previously referred to as "Yosemite Valley's Twin" is most known today for being one of the earliest Conservation fights in American History. One might even assume, it's not worth your time. Only a fraction of the visitors make it out to this secluded corner of the park. In a 5-mile moderate hike, you will see 3 waterfalls, two of them comparable to many of the icons in Yosemite Valley. I was pleased to discover a Sierra newt near one of the falls as well. I thoroughly enjoyed my time here as a quiet alternative to the busier areas of the park.