We had such good luck at our last lake in Snoqualmie Pass, Gold Creek, that we decided to try big Keechelus (don't ask me how to prounouce it) Lake. It's located off the same exit (54 - Hyak) as Gold Creek.
What intrigued me to the lake were the descriptions on various caches that indicate that many of the islands in the lake can be traversed at certain times of the year depending on water level. Sure enough, today the water was down and we were actually able to walk to one of the islands on a cache hunt.
The views of course are amazing, but the lake lacks the tranquility of Gold Creek. Due to the receding water, there is much more "brown" than green. However, the water is shallow and warm, and the kids had a ball for an hour playing in the lake.
The Iron Horse trail runs near the lake, so I assume there are some side trails that run between the two. This is also a popular boating spot, with a couple boat launches on the lake.
If I had a choice, we would go back to Gold Creek instead of Keechelus. More scenic, better trails, and more picnicking options.