I think it depends on your definition of science. Did they follow the scientific method to arrive at their conclusions? I think so, most of the time. Now, I think where they often fell short was in the "Gather data to test predictions" step. Their data gathering was limited and sometimes flawed. But that doesn't mean it's not science.
The cool thing about Mythbusters, though, is that they analyzed things that no other scientist would care to test, and sometimes those things had practical applications. For instance, every time I see a pick-up truck going down the road with its tailgate hanging open, I think to myself, "Ah ha! You are actually hurting your gas mileage, rather than helping it," because I learned that on Mythbusters.
And I loved it every time they debunked the special effects in movies and TV shows. Who else is going to do that?