This is a well constructed song using some old and new techniques. One old trick it's using as well as dropping the thick E string down to a D note, is dropping the entire tuning of the guitar down a semitone. That means that the strings are now Eb (1st-thin), Bb (2nd), Gb (3rd), Db (4th), Ab (5th), Eb (6th-thick), the guitar is still tuned normally but has the sound of being 1 fret lower. Bands do this for a couple of reasons, the first and main reason is for the vocalist. If every song is a semitone lower there will be less strain on his voice through out the night. This technique it mainly used by cover bands because the vocalist usually has to copy about 50-60 different singers styles in a night. Some bands do it just because they like the lower tones the guitar produces.
When you try to play along with the CD you will be out of tune with it because they're tuned a semitone lower, all midi examples on this page are in normal tuning.
The intro riff is easy enough to play, all I could say for this is watch out for your picking direction. Nine out of ten times your picking direction is governed by what string you're playing next. For example the first note you're picking here is 6th string open, the next note is 5th string open, it is only common sense to pick downwards when playing the 6th string because the next string you're playing is the 5th (picking towards your next string). And naturally if you're playing a note on the 4th string open and the next note is 5th string open, then pick up on the 4th string. If your picking the same string a few times over just use normal alternate (down, up) picking.
Q: Why use alternate picking for songs that are slow enough for me to pick all in one direction.
A: Even though you can pick some slower riffs all one direction you should try to use alternate picking as much as possible. Remember, every time you learn a new song you make the next one easier in some way. If you employ the correct methods on simpler songs then you don't have to worry about them as much when you attempt more difficult pieces of music. Then you can focus more on the difficult parts of that song.