Fun hike! I've done Crystal Peak before, but the trail to the lakes is its own beast. Make no mistake: there's still plenty of elevation gain on this hike, but it's a fairly consistent grade, so you know what you're in for early on.
Lower Crystal Lake is worth the brief (<1 minute hiking time) detour from the main trail, but isn't much of a destination in its own right. The upper lake is gorgeous though and well-worth the exercise. If you make your way a few hundred yards up the path towards Sourdough Gap you also get a nice little peek at the top of Rainier, which is otherwise obscured for most of the hike.
Crowds
Granted I was hiking on a Monday, but this is a solid trail if you're looking for relative solitude. My entire ascent I encountered just a couple of hikers, and in the several hours spent around the upper lake I only saw a few more people (both campsites were claimed though). I passed 19 hikers on the descent, so it was a bit busier in the afternoon, but still nothing compared to a lot of other Mount Rainier hikes.
Snow conditions
The trail to upper Crystal Lake is completely snow free at this point, so if that's your destination you won't have any problems. If you're planning to continue to Sourdough Gap though, snow is still an obstacle.
I encountered three snowfields before turning around- the first two were fairly short and easy to navigate, but the third didn't have clear footprints to follow and I couldn't locate the trail on the other side. Given the relatively steep grade of the trail I decided to make that my turnaround point, and I'm glad I did given how slick the previous snowfields were on the descent.
Bugs
The bugs didn't seem too bad during the hike itself- swatted away a couple of mosquitoes near the lake, but they never felt like they were swarming. Once I got home I noticed half a dozen or so bites though, which is more than is typical for me, so I figure it's worth mentioning.
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