The game is online. Period. You cannot play offline. However, you can play by yourself and do most of the stuff the game offers. You are not required to run around with other people. It's just that the game is made to entice you to run with others. Public events like the one shown at E3 will obviously require you to work with other players if you find yourself in one. There will also be raids and competitive multiplayer. If you just want to play through the story on your own from start to finish you can do that, though.

From what I understand, this game isn't like most MMOs where the majority of the world is open with a bunch of people running around and a few closed (instanced) areas where only you or your group exist. It's the opposite from what I've heard. The majority of the world is closed for you and/or your group but there are some areas that will be open with a bunch of random players present. Think Borderlands if it had areas where a bunch of other players can show up that you have no control over.

Hmmm. I get it. Thanks for the explanation.

Good. I still think it is just as important for an FPS to have a good single as well as multiplayer.

i'm speculating as much as you are but...

...i've seen a couple quotes along the way comparing destiny to journey.  (1, 2)   I think a critical quote is:

""It's not about stuffing as many people into a space as possible," Parsons pointed out. "The amount of players you see is design-controlled.""

i think other players will be seemlessly added and subtracted behind the scences just like in journey.  how (and if) you interact with them is largely up to you.  ignore them if you want or form a co-op group.  if you group up then you can start encountering other groups too in a more competitive fashion.   either direct competition (kill each other off) or objective compeitition (a race to be the team that gets to an objective first like taking down a large boss). 

so basically, if i just want to grind out some kills to farm some loot i can do so unmolested.  when i want to start "raiding" i can immediately shift over to MP interaction without going through any sort of a transition (exit SP, load MP, wait for lobby to load, ect.).  The PERFECT blending of SP and MP gameplay.

it sounds soo fucking amazeballz.  i'm sold on this game already.

A while ago, I read an article about about how they mentioned about Clans or something on this game, and I asked someone 'Is this an MMO?' they said no. Seems it is, no offline single player. Oh well. Maybe the industry will learn soon that not all of us want to be online all the bloody time. Even if we are connected doesn't mean we want to play with people, gaming in itself is a loanly activity, just like read and watching films, you can do both those things with people sure but majority of the time is done on your own (or with films, not talking).

Cant wait to try it, watched some previews of PS and it looks awesome.

I will have this day one. I am looking forward to this more than any other game for this year.