Comet Falls in Rainier National is really amazing. It's a busy trail but if you want a challenge you can keep going up to Mildred's Point which has one of the most spectacular views of Rainier. I think it ends up being 6 miles round trip. I would also recommend getting this book. It is has a lot of great hikes and the views never disappoint. Last summer I complete 10 of the lookouts. It was a lot of fun.
Hi Carly, I have a book called "Take A Walk: 100 Walks Through Natural Places in the Puget Sound Region" and I found a few things down here in the South Sound. Some are shorter than your 2-4 mile target, but they might still work. Point Defiance Park in Tacoma has some nice forest trails, not too long, not too hilly (I'm a flatlands walker myself). The Tacoma Nature Center has two trails for a total of 2.5 miles, level (Wetland Loop) to moderate (Hilltop Forest Loop). If you come north a bit, the Soos Creek Trails on the Kent East Hill are nice because of all the bird activity - but there are definitely hilly spots. If you don't mind a drive and want to make a day of it, head out I-90 to North Bend and make it your jumping-off point for trails around Rattlesnake Lake. If you don't mind pay-to-play, go to the Rhododendron Botanical Species Garden and Pacific Rim Bonsai Collection in Federal Way off Hwy 18. The bonsai collection is free but the RBSG is not. However, late April and early May are very pleasant in the garden! We live close enough that we're members and enjoy the garden year-round. Most of my nature trail choices are driven by whether or not there's good geocaching in the area or not.
My copy of 100 Walks is a much older 2003 version, but her newer editions are in the Pierce County Library System if you want to check them out - there are probably more options in the newer versions! Happy trails to you!