This is really nice closure and a very heartfelt gesture from Laidlaw. Even if this plot summary itself ends on a cliffhanger (again), it's more than enough.
"And here we are. I spoke of my return to this shore. It has been a circuitous path to lands I once knew, and surprising to see how much the terrain has changed. Enough time has passed that few remember me, or what I was saying when last I spoke, or what precisely we hoped to accomplish. At this point, the resistance will have failed or succeeded, no thanks to me. Old friends have been silenced, or fallen by the wayside. I no longer know or recognize most members of the research team, though I believe the spirit of rebellion still persists. I expect you know better than I the appropriate course of action, and I leave you to it. Except no further correspondence from me regarding these matters; this is my final epistle."
The last paragraph is beautifully written, and so very heartbreaking. It's fairly clear it is about the legacy of the Half-Life team and the fans of the series, and where they both stand or stood in what Valve is today. He's not only shared the plot of the game, something we've all been waiting for, but also his own story – and that makes the closure so much more intimate and personal.
It's also interesting to note that the Half-Life 2 story was never really pre-written – it evolved alongside the game, in that the story would change to suit what the game engine was capable of and what design goals the team set for themselves. The story he has shared is likely a snapshot from somewhere in time.