Graphical Overhaul- We all expected a upgrade Halo 4 graphics, but since it's still built on the Reach engine, I didn't expect this. The lighting is the thing stuck out the most to me, and damn does it look good. They also did new models for all returning assets.
Sound Overhaul- 343 threw out all the old sounds and are starting from scratch. In his Frank O'Connor interview, Ryan McCaffrey described them as more punchy then ever, which is extremely evident in the gameplay footage they show. And for game music nerd like me, 343 has hired a new composer to take the soundtrack in a new direction
Unexpected New And Returning Mechanics- I, along with many others, did not enjoy sprint in Reach. However 343 felt it needed to return to the series, which is especially perplexing since 343 took sprint out of the Halo reach MLG playlist because of the outcry against. Something else shown in the the ViDoc is an actor doing a hurdle over a rail. Since this is an early look we don't know for sure, as of now it appears they will be adding cover hurdling ala Battlefield 3.
Sandbox Story- A word that comes up allot in both videos is "sandbox". I don't work for 343 so I can confirm, but I do not think Halo 4 will be a sandbox on the level of Grand Theft Auto. The first thing I think of is the originals second level simply called "Halo". Way less linear then any other FPS, but still controlled in a level, instead of roaming a whole world.
Better Story- Until now, 343 and it's employees has been mostly involved in creating Halo stories outside of the games, and they want to bring their storytelling prowess to Halo 4. Josh Holmes, creative director of Halo 4, said, "threat that is unlike anything Master Chief has faced before". Combine that with their focus on a more cinematic game and Halo 4 is set to have the most compelling Halo story to date.
The BR is Back!- I really don't need to say much more. Most peoples favorite weapon is returning after a two game absence. However O'Connor has said one-shot weapons similar to the DMR will still be in the game.
No Bloom- The biggest point of contention in Reach multiplayer was bloom. Players didn't exactly hate the concept, but the fact it wasn't done well. It made the game feel to random and was removed from certain playlists along with sprint.
Maps from Scratch- Reach was the first Halo to have multiplayer maps taken from its campaign, and it didn't work out. Reach had pretty bad maps. So 343 is making maps from scratch, although some will be set in the same as certain campaign missions.
Multiplayer Story- Who needs it? No one. But 343 added it. "We have a fairly compelling and fairly convincing reason why red spartans can fight blue spartans"- Frank O'Connor.
Customizable Spartan IV's- For those who don't know: Master Cheif is a spartan II, the ones in Reach (minus Jorge) are spartan III's, the spartans in Halo 4 multiplayer are spartan IV's the newest breed. 343 has said you will be able to customize the spartans past just armor like in 3 and Reach. They haven't said what, but they said it isn't just going to clone COD.