Exercise 3 represents the "Symphony X" part of the song. I like playing riffs that somewhat tease the listener, letting them know that there's an even bigger riff coming their way next. So I like to think of this part of the song as a build-up to Exercise 4.
When you look at the tablature, you'll notice that we have a lot of 8th note and quarter note rests. All of those rests must be extremely tight, meaning total silence for the duration of the rhythmic value. When you watch the video, notice how I use both my left and right hands to mute the strings during the rests. I recommend that you do the same whenever possible.
Get those rests nice and accurate, then I'll see you in Exercise 4.