Destiny's Patch 2.0 is live and already players can see the sweeping changes to the games sytems, UI, and gameplay. Guns have been buffed or nerfed, the levelling system has been revamped, and behind the scenes changes have been put in place to make the mechanics of the game run smoother than ever. 

The changes are too numerous to list out here, but Bungie has built a very comprehensive set of patch notes for the release that covers every little detail of the update's effects. You can go over it if you've got some free time here.

Some of the major tweaks include a more robust quest system that tracks your missions and allows you to re-play previous ones easily. A new level cap of 34 that can be reached by anyone (the Taken King Expansion will raise that to 40), not to mention the removal of light levels as the main source of player progression which will now be replaced with the more traditional XP levelling system that was used from lvl 1-20.