I myself wouldn't necessarily agree with the specifics of what Mike wrote, but can understand where he's coming from. To me I always saw it like this:
First gen is the original Dungeons & Dragons and D&D adaptations that are like as he said-- the slow move from wargaming into playing a character in a fantasy genre. Building dungeons and running through dungeons is the order of the day. This is probably '75 through the early '80s through the publishing of both Basic and Advanced D&D.
Second gen starts in the early-mid '80s where other RPGs are being invented and designed that don't mechanically follow D&D's formatting, plus begin to involve all kinds of other genres besides fantasy. So our GURPS, Toon, James Bond, Paranoia, Champions and so on. They are all RPGs, but no one would ever say they were trying to mimic D&D in any sense.
Third gen starts where he mentions, around 1991... but for a reason different than what he said. To me it was the advent of Vampire: The Masquerade and the increased narrative and story-heavy types of game. Games that never expect you to use grids or miniatures, games that do not have a combat-focus, games for whom game mechanics are not the primary method of interacting with the game. Instead, its the in-depth stories being told together by the players.
Fourth gen is where I agree with him on the 2000 3E advent, which is all about going back to creating rules to mechanically create whatever type of character you want. It also is the advent of the OGL and d20 system, allowing for an inordinate number of companies and people to design more and more and more products to extend the design of a character. Splatbooks all the way down.
Fifth gen? I do agree with him that we are in it, but I think the reflection point of it should be described differently that what he suggested. Mike said it's about new games making things easier for GMs to run... whereas I think the turn is reallly about the rise of Indy RPGs leading into the advent of Actual Play. With games that are more about character personality and character emotions and character relationships taking center stage, with combat and mechanical "character builds" no longer the focus. Players of this generation now are concerned with the interactions of their characters to each other and to the characters and essence of the worlds they are in, just like the actors and improvisors they watch playing RPGs online. And part of that is because the watching of the "board game" part of RPGs online through Actual Play is not the fun or compelling part and not the reason people tune in. Instead, it's roleplayers interacting vocally and emotionally with each other. Indy RPGs led the way on that, and 5E was light enough that it could be run in that manner successfully (even though it's not designed around the Indy RPG narrative aesthetic.)
And to me this has nothing to do with the attempted revocation of the OGL... as Indy RPGs had already begun to gain steam in the late 2000s and which lead to Actual Play in the mid 2010s-- all before the OGL fiasco.
