Well, granted that you have a sly avatar I would hope that you already have a ps3 and ps+, so that part is out of the way, if not, then your first difference is clear.
1. Lots of free games on ps3/vita/exclusive ps4 access
Another difference would be the games.
2. PS4 has a strong lineup, though probably not as strong as xb1, but also is backed by every major indie dev and through self publishing, will see more and more unique content that isn't blockbuster fps games. Sony has also stayed consistent with its publishing through the ps3 years, and while their big titles sell slightly less, they have a bigger catalog. So this one is 'blockbuster AAA games' vs 'a few less blockbuster AAA games and a lot more variety'.
Another difference is in the camera
3. Kinect 2 vs optional psEye3.0. Both will likely function similarly.
Price.
4. 400$ vs $500. and the difference in multiplayer cost over the gen is roughly a brand new game.
Another difference is the controller
6. Trackpad and share button vs rumble triggers.
This is really just your call. Easy functionality and new control mechanism as opposed to new feedback.
A lot of other things are going to be the same:
Cross chat
Tablet devices coming out
Cloud and streaming access
Media stuff like Hulu, netflix
Used games
Digital Sharing
Video upload (sharing)
The only other difference is what the consoles look like and their relative size.
