Pantheon is an amazing challenge for people who already like raiding. Unfortunately for the casual player, its going to be fairly impossible to do 8 encounters in a row while 20 under level.
Onslaught is extremely boring unless you like shooting ads and killing mini bosses for an entire hour, but the rewards are fun.
The new crucible maps are fun but the state of the crucible isn't, still props i guess.
Several renewed exotic missions are back, which is great but I wish they wouldn't remove them to begin with.