I live in Washington and hike in Mt. Rainier National Park all the time. I've only been hiking there for the 1 1/2 years I've lived here and love the experience.
There are plenty of trails in the park and great views. I usually hike early in the morning because there are less people out. Even hiking mid-morning you can hike on trails that aren't crowded.
Some of the trails are very popular and bring the usual suspects out, but only a few of the trails get crowded during peak season. I once saw a woman pushing a stroller w/child up a trail while her husband carried the big ice chest. For the most part, rangers are visible and don't put up with the stupidity of the weekend warriors.
For trail conditions at Mt. Rainier go to
www.nps.gov/mora, then click on activities, then hiking, and click on trail conditions. They update every week on Thursday during the summer, and periodically during fall and winter.
If you have specific questions you want answered e-mail me and I'll do my best.