Is it possible to use EV3 sensors and motors with the NXT intelligent brick? I've read that the EV3 is backward compatible with NXT motors and sensors, but does vice versa work as well? Is the NXT forward compatible with EV3 sensors and motors?
Short answer: you can use EV3 motors with NXT, but you can't use EV3 sensors on NXT. NXT sensors and motors work with EV3.
Detailed answer: read Laurens Valk paper.
The NXT works fine with EV3 motors, and will read them as NXT motors. EV3 sensors, on the other hand, do not natively work with the NXT, with the exception of the touch sensor.
The reason for this is that, touch sensor notwithstanding, EV3 sensors use a hardware communication protocol called UART, which is not supported by the NXT. The NXT only supports analog and digital I2C. The EV3 touch sensor works with the NXT because it's an analog sensor, unlike the other EV3 sensors.
That being said, it is possible to make EV3 sensors work with the NXT via an EV3 sensor adapter:
An adapter is required for each sensor port used. Unfortunately, it's not currently supported in NXT-G; just in NXC and EV3-G.