Both you and EnragedTemplar answered your question. Destiny has two major facets to it: [b]Co-operative Play[/b] (PvE): social shoot 'n loot exploration with story-missions, public events, raids, and strikes. Some elements more free roam, others more linear. [b]Competitive Multiplayer[/b] (PvP): You compete against other players for loot and glory. Where Destiny is different, than let's say Halo, is that all these activities are woven together into one online, persistent world. Where people can drop in and out seamlessly. You have one character that carries over (and across) into all modes of the game. Many barriers and figurative walls have been taken down.

Campaign is an automatically co-op experience. Competitive is the typical, kill the enemy team stuff. They are two separate instances, though competitive mp is couched in the fiction of the Factions.

[quote]Do you simply compete for score in a sort of Borderlands-esque experience,[/quote] cooperative play [quote]or can you actually play against each other in teams, a-la Halo?[/quote] competitive play you explained it yourself! any kind of ranking system for ranked style of play has not been announced at this time.

Maybe this will help