Watch the Example 23 online guitar lesson by Brad Carlton from Guitar Lab: Boogie-Woogie
This last example is very demanding on the fretting hand. Dmaj9/A (or A add9 add4), A6 sus4, A13 and back to A6 sus4. A mixolydian is the source and voices 1, 2, and 3 form a cluster utilizing intervals of seconds. That's why it's hard to play and sounds unusual. But these clusters would be easy on keyboard. Obviously for a guitarist, intonation is the greatest challenge with this example so imagine how much better you'll be able to control your intonation with "normal" voicings if you can play this one in tune.