stiraq, when i started to play game players would adjusted their own shield to incoming damage from players sadly that game is dead and no one even uses their own shields according to who is hitting you.
in pve you make the most out of combos by exploiting unshielded side, its not my fault people dodge this versatility and go for combo rotations wich is a mistake.
each class has indeed a few combos wich are priority because they enhance other follow up combos in some way, or simply because they debuff your target so you can deal better damage.
i leave funcom's tutorial its funny video feels like watching dharma videos from lost :P
http://www.youtube.com/watch?v=zIAsPkrLGK8