The generations of Intel's integrated graphics Which among Intel's integrated GPUs depart from their predecessors in a major way? Which are merely incremental improvements?

BACKGROUND

Intel integrates GPUs with many of the processors they sell. With each generation of processors (Ivy Bridge, Haswell, Broadwell, Skylake, Kaby Lake, etc.), Intel updates the graphics architecture. Much is written in the popular press regarding each of these: does your favorite video game make only 98 frames per second on the latest, or does it achieve a previously unheard-of 99? Bar charts are published, and so on.

None of the articles, or practically none, seems to grasp the underlying technology. I would be interested to learn whether Ivy Bridge, Haswell, Broadwell, Sklyake, Kaby Lake, and so on, are each merely incremental improvements in the same, basic graphics architecture, or whether, say, Broadwell (or Kaby Lake, or whatever) was an entirely new design.

I would likewise be interested to learn if one generation had been upgraded over the previous in a way which made OpenCL-type usage much more practical or capable.

Apparently, Broadwell was the first capable of Vulkan, but I do not know whether this capability represents a fundamental architectural change or if it's just a driver issue.

Most of the popular press seems pretty clueless at this technical level. Can you shed any light?
You want to look up "Intel Graphics Developer Guides", they are quite thorough.  Here's a link to the latest:

https://software.intel.com/sites/default/files/managed/22/6d/6th_gen_graphics_api_dev_guide_dec_2015.pdf

And here's the architectural Cliff Notes for the past five generations of Intel GPUs:

"In several important respects, the 6th gen Intel Core processors' graphics hardware architecture is similar to that of 5th generation Intel® CoreTM processors"

"The graphics hardware architecture of the 5th gen Intel Core processors is similar to that of the 4th gen processors."

"The graphics hardware architecture in the 4th gen Intel Core processor is similar to that in the 3rd gen processor."

"The new generation of microarchitecture, codenamed Ivy Bridge, provides another jump in functionality and performance over Sandy Bridge microarchitecture."

"With the introduction of the Intel microarchitecture codenamed Sandy Bridge, the graphics processor has moved onto the same die as the CPU, and is now referred to as “processor graphics”. In addition, processor graphics has enjoyed numerous architectural improvements that yield significant performance improvements over previous generations of Intel® integrated graphics parts."