This is an amazing trail for many reasons! First and probably most importantly, as the name says, this trail is a wash, which means there is tons of wildlife along the trail (animals love to hangout in washes). Also, this trail connects with many other trails, if you want to extend your hike. Another great thing about this trail and many of the others is that they loop, so you get to explore new ground the whole hike. At the trail head there are restrooms and sometimes volunteers with information and maps. They also have guided educational hikes on the Lost Dog trail (generally on the weekend).
I usually mountain bike this trail; it has some switchbacks and a bit rocky in some areas so I wouldn't necissarily recommend that for everyone. The Ringtrail loop is a bit easier for mountain bikers. Lost Dog does get busy during the tourist season and most weekends. If you are mountain biking, to avoid a crowded trail, I would recommend doing it early in the morning, on the weekends, or during the week.