Fast becoming one of my favorite early hikes, not too far from Seattle, and clearly well loved given the number of reports. So I'll only add a few notes. Firstly, don't make any turnoffs from FR 12 until you actually see the sign for the Recreation Area (FR 13); I seemed to have made the same error last year.
This is a superb hike, moderate elevation gain, and has many view stops along the way to rest or eat. There are places, at least at this time, to refill bottles before reaching the lookout. Now is a good time to go. As of this writing there are still some snow patches in the meadows and covering Twin Sisters and other distant mountain ranges that highlight the beauty of the region. Wildflowers are not plentiful but some are appearing, especially on the western slope leading to the lookout. The heather is spectacular in dark pink and stunning white, even more so during early evening hours. The tarns are photo-perfect with just a bit of fast-melting snow remaining. Look far below to the turquoise snowmelt pond visible to the left in the last 1/8 mi of trail. Surprisingly, there were few people on the trail on a weekday. And no bugs at all on a somewhat breezy day (once altitude is gained), perhaps just the luck of the day.
Driving back along Highway 20, a large herd of elk was grazing on open land near one of the small towns.