Overall Rating: 4.6 (of 5)
The first three measures just repeat a three string chord shape which is moved down one fret each measure. Really try to pluck those strings hard so that the strings slap back down against the body of the guitar. Sometimes I use the sides of my fingertips, sometimes I dig down under the strings, use whatever technique works and sounds good to you.
The fourth measure contains a classic blues lick in the key of E. Slow it down until you get the lick to really flow without struggling to keep the thumb going. Eventually the thumb will just pluck right along without much conscious thought at all.
The first chord is an E7. The second chord is an E diminished7. The third chord is an Am(#13)/E. That's a tense chord, and really bluesy when it resolves to E in the fourth measure for a nice little lick. Keep in mind that this sort of thing can be generated by moving the chord shape as I have done, but this was not without some thought. If my chord shape had an E in it, and I moved it down a half step, the D# would have clashed with the E in the bass. A major seven is not very bluesy, blues music tends to use the b7.