Bungie released a new teaser for Destiny: The Taken King which shows a lot about the upcoming expansion and what you can expect from it. The light levels still exist and the more you have determines the attack and defense potential of your character.
The base level has been increased to 40 from 20 which goes to show that this is a massive expansion. There are new exotics obviously and you will have to do a lot of stuff to get them compared to before where it was simply an RNG drop.
There will be quests and you will be able to carry up to 32 quests which kinda hints that there will be a lot of quests. There are other things also and you can check out the video below that breaks down the teaser trailer and tells you all that you need to know.
More information on these things will be revealed today by Bungie via a Twitch stream so stay tuned for that.