I'm trying not to get too hyped because it's probably going to be Destiny Redux and have like 5 hours of content plus it's still a few weeks out.
With Bungie never releasing Destiny on PC, even with a supposed 10 year life cycle on last gen systems, I never played it... So, obviously no comprehension to it.
In the closed beta you could get to level 7, starting from level 4, by pretty much doing every mission on your map... lvl 8, max level for the beta, you had to kill allot of random stuff too (Exploration XP helped also). Max level is 30. That doesn't sound very high but it took me, if I remember correctly, about 2-3 hours to hit that cap on my second character.
There is also a Dark Zone level, which is hidden to all but yourself, that also maxes at level 30. 12 in the beta... I thought it was easier to level but it can also lose levels if you do allot of stupid stuff. The higher this level the better the gear drops in the DZ will be and also what you can see at DZ vendors.
Being 30/and close to DZ 30 resets the DZ too a higher tier of enemies so you don't out level any of it and have an extremely large zone to run around in. (Hopefully the normal area re-level also but I've not heard any talk of that.)
Oh, each story mission will have three difficulty settings at release.
Granted, I have no idea what that means for content... but loot driven games. You're going to see all of the content allot and the best places to get loot you'll see a ridiculous amount of times.