KEG: A fantastic battle between two amazing tacticians. A treat for all of us. Sad to say, however, I think the commentators have mistaken exactly what happened and where Tchigorin went wrong.
I agree with Knight 13 that Tchigorin's 12...Bh4 and 13...BxN are not the theoretically "best" moves, but as bengalcat47 correctly notes, Tchigorin preferred knights to bishops. Thus, I think the plan adopted was correct for Tchigorin. According to Fritz, Tchgorin's plan was only slightly inferior to 12...a6. Tchigorin had been following his methods for many years and had won many great victories playing this way. Like all of us, it was best for Tchigorin to seek positions in which he was most comfortable and in which his tactical genius could best be brought to bear. Indeed, it is thanks to Tchigorin's unorthodox style that we have this fascinating game to analyze and enjoy.
PawnandTwo is also correct that 20...b6 was somewhat better than the immediate 20...Qh4, but Tchigorin's move was also OK and the position was still approximately equal.
The real struggle began when Tchigorin decided to hang his a-pawn with 21...f6 and pursue his mind-boggling king-side attack. Tchigorin could have simply played 21...Ra8 to avoid the "a-file virus" Knight13 mentions, but had he done that, he would not have been the Tchigorin we all love and enjoy. Predictably, Janowski accepted the challenge and took the a-pawn with 22. Qxa5, and the battle was on.
The resulting complications were so deep that it took Fritz a very long time to settle on a conclusion. In fact, the pawn sacrifice allowed Tchigorin chances, but gave him the worst of it, though probably not a lost game.
Janowski's 24. g3! was pretty. The Tournament Book suggests that Tchigorin had missed this move. But I'm not so sure. After Janowski's 25. Rg2, the Tournament Book contends that Tchigorin needed to play 25...Qh4 to survive. In fact, that line is bad, and Tchgorin's 25...Qh3 contained a little trap that both Janoswki and the Tournament Book commentator (Hoffer) appear to have overlooked.
Janowski could have maintained his edge with 26. Bf4. Instead, he grabbed a second pawn with 26. Qxc7. As I suspect Tchigorin had noticed, this pawn snatch gave his King-side attack new life. After 28. QxR check, Tchigorin had to play 28...Kf7. The power of his king-side attack after that appears to have been overlooked by everyone. It even took Fritz a very long time to recognize that Tchigorin now has at least equality, in part because White's Rook is potentially hanging on a1.
Sadly, and after all the fabulous ideas in this game, Tchigorin took his eye off the ball for a second and played 28...Ne8. After that, Janoswki's 29. Bf4 was murder, and what followed was little more than an execution.
The losing move in this game was 28...Ne8. Apart from that, both players deserved a brilliancy prize for this game in my book.