While, I still haven't been in April, going to the park the first week of May was also ideal. The high Sierras were still desolate with snow, but the valley was already warm and green. While there were still more people in the park than I would have preferred, it was not the Disneyland-esque shitshow that is Yosemite valley in the summer. We were able to reserve a campground spot with less than a week's notice. We only saw 4 other people the entire snowy hike to May Lake, which was pristine and shimmering under a think layer of ice. The Yosemite Falls hike in the valley, one of the busiest trails in the park, was sparely populated enough that we didn't have to leave at dawn to beat herds of hikers choking the path. We even found immediate parking at Glacier Point, so we could take the easy route up to Sentinel Dome on the last day.
TLDR: First week of May is a great time to visit Yosemite, but be prepared for snow in the high mountains.