Got my first hands on with the PS4 today. this is what I thought.
I got to play Tomb Raider, AC4 and Battlefield 4.
all three of these are available on PS3 but I have only played Tomb Raider on the previous generation.
Battlefield was by far the most impressive visually. textures and lighting in particular were amazing. draw distance didn't really play a part as the two maps I played on were pretty small, but over all I was impressed graphically.
Tomb Raider was leaps and bounds above the PS3 version visually. I stood for a full minute in a puddle just watching the effects on the surface of the water. truly astounding. I didn't get much of a chance to go beyond the graphical changes as I only played it for a few minutes.
AC4 was an interesting mix. Graphically, it felt over textured, which is pretty common for ubisoft games even on PS3. but I don't expect to be able to see the grain on a timber board 100 feet away. It just felt like they were trying too hard to make it "Next Gen". having said that, It is a beautiful game visually, with some amazing views. game play wise (which I doubt differs from the PS3 version much, If at all) I was impressed. The locations I got to visit were much more fun that AC3 to free run through and the naval battles felt much more complete and a great deal better thought out.
The thing that stood out the most though, was the controller. The change between controllers from PS2 to PS3 was nonexistent IMO. this control is a huge step forward. I would even say it is more comfortable that the Xbox 360 control. As someone with degenerative arthritis in my hands, I played for about 4 hours and I could still type all of this. Happy days.
Once there are some games I am really excited about, I will be getting one.