Do this hike! It is a gem - one of our favorites at Mount Rainier!
The road to the trailhead is okay - washboarded and a few big potholes. Nothing that our truck couldn't handle easily, but allow extra time for low-clearance vehicles. We got to the trailhead at 9:30 am and it was packed. Not surprising on such a beautiful day. Most of the hikers must have done Spray Park as the Tolmie trail wasn't packed. That is not to say that it wasn't busy - there was a steady stream of people up and down all day.
The trail climbs steadily from just below Eunice Lake, levels out a bit in the lake basin, and then picks up again on the last stretch to the top. But the last stretch, while intense, goes faster than one would think. Do not let the sight of the little lookout building looming high above the lake make you think it isn't worth the climb. It most certainly is. The view from the top is, in my opinion, the best at the park.
There were a couple of bears hanging out in the trees on the other side of Eunice Lake. They had quite the gathering of paparazzi awaiting an appearance, but they stayed out of sight. We caught a quick glimpse of one of the cubs, but that was it.
My GPS measured the hike (from the Lakeside Trail trailhead at Mowich Lake closest to the latrines to the top and back) as 6.35 miles and 1566 feet of elevation gain. Our 5 year old was a trooper and did the entire hike, but it seemed to be more difficult for her than Glacier Basin (White River campground). It is tough but worth it!