There are a few key breakthrough nodes that aren't simple die shrinks. 28 nm and 14 nm are some of the critical nodes.
14 nm is the first FinFET process which many companies are unable to do because it is more challenging in many ways: it has a disproportionately smaller minimum feature size than the planar process - the fin width. The diffusion rate of photoinitiators in the resist becomes important at such small resolutions. This means hard mask rather than polymeric resist, which introduces challenges in resist development and removal.
28 nm and associated classes like 20 nm, 22 nm, etc on the other hand is the smallest planar node. It combines all the experience of prior nodes: high k dielectric replacing gate oxide, tungsten gate metal, copper interconnect, SiGe use, strain engineering, immersion lithography, etc. It is basically the highest development of the prior processes in development since the 1950s.
Each of these critical nodes has a ton of companies drop out and no longer keep up with the leading edge.
7nm is also a key node. It's where transition from DUV to EUV is needed; it's also a sweep spot node in terms of cost/performance ratio, after which the cost increases much faster than performance.