I'm loving it so far. The main menu is different but easy to navigate. I like how you can charge controllers and download stuff while the console is in "standby" mode.
Haven't really noticed a decrease in load times yet, thought I would.
The graphics are amazing, of course. 1080p is awesome, everything is so sharp and clear. The particle effects (dust and debris flying through the air, etc) are spectacular.
The Dualshock 4 feels really, really good. The grips are longer and the sticks are farther apart, so it fits better in your hands. The triggers are good, though its taking some getting used to using R2 to shoot instead of R1.