Definitely worth going if you don't have much time.. They cover most of major sights of D.C., give plenty of time everywhere, except the Aero Space Museum. This place is huge and packed with interesting stuff which you don't have enough time to explore.
Our guide (English only speaking group) was amazing and very informative. His name was Matt.
My advice is to arrive early so you get the nice front seats in the bus and you'll be able to see everything clear.
A long day of bus travel - but a great way to get a taste of Washington, with a quick tour of all the key sites. The visit to Madame Tussaud's wax museum was a little unnecessary and we would have preferred that time to be added to the visit to the Smithsonian museum.
It was a great tour. Even though it was a day trip we didn't feel rushed at all. We even got to see a little extras along the way cause there was no traffic on the roads. The tour guide was excellent and the people friendly.