Back in the 80's I practically lived in the Park on weekends. You can spend days and rarely see much wildlife, or you can be falling over elk and bighorn sheep all over the place. I've watched coyotes hunting, I've been just 3 feet from a porcupine which was quite unimpressed by me. You can find a use for anything from ultrawide to 400mm telephoto.
That time of the year, access depends a lot on the snowpack. Trail Ridge Road is usually open by then unless there is a late snowstorm while they are trying to clear the road. I can't remember the last time that they didn't get it open by Memorial Day.
There are some great hiking trails in the Park. If the trail is passable, you have to take the hike up Glacier Gorge (trailhead is on the road to Bear Lake, about a mile before the parking lot) to The Loch, and then backtrack about a mile to the Mills Lake trail and head up to Mills, Jewel, and Black Lakes. At Black Lake you are at the foot of the west side of Long's Peak, 14,000+ feet, only you are several thousand feet below the summit. This is one of the most scenic areas of the park.