Welcome to Disneyland. The Yosemite Falls Trail vies with the Mist Trail for being the most crowded trail in Yosemite National Park, which surely makes it one of the most crowded trails in America. If you want some solitude on this trail, you'll have to go very early, very late or during the winter when the trail is closed (and you could get fined for hiking it, but that didn't stop Benjamin Burner who has some great pictures of the Falls Trail in winter). That said, you will have the best views of Yosemite Falls and excellent views of Yosemite Valley. You can also extend the hike up to the summit of El Capitan or Yosemite Point, where crowds will diminish dramatically. Plus, everyone has to hike it once (and I hike it many times every year just because it's convenient and an excellent workout).
Begin at the Camp 4 parking lot and walk straight back to the Valley Loop Trail and the Falls Trail intersection. The trail begins in oak forest with a long set of switchbacks of the old style - short and relatively steep. If you're not fairly fit, you will likely suffer here, but it is not *that* long. This is the least pleasant part of the trail. After a bit, you'll start to cross some washes (dry after about mid-June) and you'll know that the worst of the switchbacks is over and soon you'll start to reach relatively frequent viewpoints across the Valley. When the trail starts to get sandy, you'll know that you're getting close to Columbia Point, which is an excellent place to stop and take in the view and have some lunch. Columbia Point is almost exactly one third of the way to the top by time (somewhat less by distance). Take however long it has taken you to get here and, if you continue at a similar pace, that will give you a pretty good idea of how long it will take you to the summit.
After Columbia Point you have just a couple more sandy switchbacks and then the trail will flatten out for nearly a mile with a bit of up and down until you get into the valley cut by Yosemite Creek. Here you get your first views of Upper Yosemite Fall. At this point, pay attention and look for a spur that goes off to the right where the trail turns left. This is the so-called "Oh My Gosh Point", a lookout with the best views on the entire trail and a rail protecting the vertiginous view (but hold onto your children!). From Oh My Gosh Point you will look straight down on Lower Yosemite Fall and straight across at the Upper Fall and see almost all of the middle cascade. Once back on the trail, you'll soon pass the middle winter closure gate. At that point you are almost exactly half way to the top by time. You also have a nice flat section with views of Upper Yosemite Fall.
From here you go back to switchbacks, but now through open chapparal. On the bottom it can range from hot and dry to pouring down mist, but usually it's just a pleasant cooling mist. As you hit the first switchbacks after the flat section, another spur goes straight where the trail turns left. A short little walk will get you out of the trees and give you an excellent close-up view of the Upper Fall.
Once you hit the manzanita scrub, you'll have no shade and this can be oppressively hot in the summer. Again, it doesn't last that long and what you see is what you get: there's no false summit and you can judge by the top of the falls how high you have to go.
The winter closure gate marks the end of the climbing. From there it's just a relatively easy quarter mile to the lookout. Those who are afraid of heights should be forewarned: the steps down to the lookout are narrow and exposed. Also, stay away from the water. In the summer of 2005 an Irish tourist wanted to get a picture of himself close to the edge. He slipped and went over the falls to his death. This is a safe place, but use some common sense.