Click on the images for a larger (readable) version.
For the tl;dr crowd:
- Sims will now experience different emotional states which will "unlock" different interactions/actions.
- Moodlets are still part of the game.
- A Sim's environment will contribute to their emotional state. (Ex. an inspirational painting in a room can cause a Sim to be more creative).
- You can purchase furniture from an "Ikea-like catalogue".
- A Sim can be so happy that they laugh to death.
- There will be new creation tools for custom content.
- New advances in group behavior-- multiple Sims can now interact together in a more natural way.
- Players now have control over groups of Sims-- they can tell the group as a whole to do something together.
- MULTITASKING! Sims can now do things like drink while eating, watch TV while on the treadmill, interact with other Sims while on the treadmill, etc.
- Create-A-Sim has been totally revamped so instead of sliders, you drag and drop on the actual Sim to change how they look (ex for a Sim with a longer nose, grab his/her nose and pull it to make it longer).
- Sims can add hats to their outfits.
- In Build Mode, you can now build a room, then pick it up and move it to a different spot. Blueprint mode will also be available from the start, but you will be able to tweak it by moving walls, etc.
Source: Screenshots taken on my Nook HD+