Ps4 – DualShock 3 usability on PS4

It is possible for PS3/4 games to be Cross-Play but it is not the default. You will have to check whether each specific game supports PS3/4 cross play as it's up to the developer to implement.

I decided to buy a Dualshock 4 and see for myself what works and what doesn't.

First off: As promised, the Dualshock 4 works on Windows without the need to install additional drivers.¹ Connection is established via a Micro-B USB cable, or via Bluetooth on computers with a Bluetooth receiver. (Hold down the Home and Share buttons together for several seconds to enable Bluetooth pairing mode. The light bar will continuously flash when pairing mode is activated.)

Game support is extremely lacking. The Dualshock 4 is a DirectInput device while the Xbox 360 controller uses XInput, which is the only API that most - if not all - modern games use. In order to use the Dualshock 4 in games that only support the Xbox 360 controller, a wrapper is needed². Here's to hoping Sony will release drivers to add XInput support to the Dualshock 4.

As for the default key-mapping; even if games accept input from the Dualshock 4, you might want to calibrate the controller to match the Xbox 360 controller's key mapping.
Matching inputs are:

• Left analog stick: main X/Y Axis
• D-Pad: Point of View Hat
• Y/: button 4
• LB/L1: button 5
• RB/R1: button 6

The Xbox 360 controller uses 3 Axis and 2 Rotations as input for its two analog sticks and 2 triggers; the triggers both share the Z-Axis.
The Dualshock 4 on the other hand uses 3 Axis and 3 Rotations for the same.

According to Windows' very own Game controller settings:
The Xbox 360 offers a total of 10 buttons³.
The Dualshock 4 offers a total of 14 buttons⁴.

¹: Tested on Windows 7 and 8.1
²: I found one such wrapper here
³: Excluding the home button, which does not seem to map to a controller input
⁴: 2 buttons are mapped to the L2/R2 triggers, which are also mapped to the X and Y Rotations