KEG: Grandpa jo has identified most of the key elements of this game (and has done a much better job of commentary than the Tournament Book has on this game).
A)Lee's Stonewall is indeed the key feature of this game. I don't much like this set-up as White and would have much preferred c4 for White on move two or move three, but Lee demonstrates here how to use the Stonewall as a weapon.
B) Given Lee's choice of opening, I agree with Grandpa jo that 8. Qb3 is best. It posed questions for Mason (e.g., what to do about the b7 pawn) that he did not solve properly, and seduced Mason into two sets of minor piece exchanges that led to the opening of the g-file. This open file--as the game went--proved lethal to Mason. But, had Mason kept his wits about him, Lee's plan should not have led to much. Of course, that's easy for me to say, since I wasn't the one staring down at an open g-file with White's heavy pieces poised to massacre my king!
After the minor piece exchanges, Mason should have avoided the threats to his b7 pawn as well as that of the open g-file by the simple 10...Qh4+. He could then have castled Queens-side and pretty much stifled Lee's obvious threats. Instead, Mason played the weak 10...Rb8, ending his chances of getting refuge for his king on the Queen's wing and essentially committing himself to castling into Lee's open g-file. This should still not have been fatal, but now Mason had to play with great care.
C) I disagree with Grandpa jo about 12...0-0. Once Mason had opted for 10...Rb8, I don't see that he had much choice. It doesn't look like much fun from Black's perspective, but Mason could definitely have weathered the storm that he unleashed by his 10...Rb8.
D) 16...c6 is indeed passive as Grandpa jo notes, but once again, it was not fatal (much as I would have preferred 16...Qd7 if I had to defend this position).
I agree with the Tournament Book that Mason's serious problems began with his weak 18...Kh1. Here I agree with the Tournament Book that 18...Nd6 was best. Waiting one move to play Nd6 was thoughtless, since he gave Lee the chance to push his e-pawn with 19. e4 and 20. e5 and chase the Knight away immediately.
Once Lee played 19. e4, Mason had to abandon the Nd6 idea and defend with 19...h6. He would still have had a playable position.
After Mason's 19...Nd6 (one move late!) he was toast. After 20. e5 Nb7, Lee made what in my view was the most beautiful move of the game in the following position:
Here, Lee played 21. Rg6 !! completely paralyzing Lee's game and setting up a winning combination. Had Mason taken the offered Rook, 22. hxg6+ would of course have been a killer.
After Mason's actual move 21...Qd7 (best) Lee's 22. h6 was overwhelming. Taking the Rook with 22...hxR would have been crushed with 23. Qxg6. Mason's only prayer of salvation would have been to try 22...Ba3. Mason's actual move 22...Rg8 opened the floodgates. Here was the position with Lee to move after Mason's 22...Rg8:
It was here that Lee played the brilliant 23. Bxf5 lauded by Grandpa jo. Had Mason now taken the Rook with 23...hxR, it would have been mate in three for Lee beginning with 24. Qxg6. Mason's actual move, 23...exB allowed 24. e6. I agree with Grandpa jo that it was now time for Mason to resign.
The only item of interest after 24. e6 was Lee's quiet 28. Kd3. The game was won anyway, but I find this kind of Karpov-like move especially pleasing.