Here are the highlights:
A 1.5GHz quad-core 64-bit ARM Cortex-A72 CPU (~3× performance)
Choice of 1GB, 2GB, or 4GB of LPDDR4 SDRAM
Full-throughput Gigabit Ethernet
Dual-band 802.11ac wireless networking
Bluetooth 5.0
Two USB 3.0 and two USB 2.0 ports
Dual monitor support, at resolutions up to 4K
VideoCore VI graphics, supporting OpenGL ES 3.x
4Kp60 hardware decode of HEVC video
Complete compatibility with earlier Raspberry Pi products
Switching to USB C for the power input gives them and addition 0.5 amp of power but requires new power supplies.
https://www.raspberrypi.org/blog/raspberry-pi-4-on-sale-now-from-35/