The original iMac family has been an unabashed consumer-centric machine with admirable processing performance, and passable graphics (even offering dedicated GPUs in some configurations). However, the iMac Pro throws everything but the kitchen sink at the all-in-one form-factor, including Intel's current Xeon W series of processors that were designed for mainstream workstations.
The iMac Pro will be available in 8-, 10-, and 18-core Xeon SKUs, offering a total of 16-, 20- and 36-threads for completing your most intense multi-threaded applications. The machine includes a 27.5-inch display with a 5K resolution, which is driven by AMD Radeon Vega graphics cards (up to 16GB of VRAM is supported on iMac Pros).
Given that this is a pro machine, you can configure up to 128GB of DDR4-2666 ECC memory, and up to 4TB of SSD storage. Other niceties include 802.11ac Wi-Fi, Bluetooth 4.2, 10Gb Ethernet, dual Thunderbolt 3 controllers and a UHS-II SDXC reader for your D-SLR memory cards.
The base $4,999 system comes with an 8-core Xeon processor, Radeon Vega GPU, 32GB of ECC memory, and a 1TB SSD. One thing to keep in mind about the iMac Pro, however, is that you throw upgradability out the window. However, if you're in the Apple ecosystem already, you should be used to that downside.