Noted by both Alekhine and Capablanca, Janowski’s play is inconsistent to his actual strength. A little passed his prime, he lost a lot of games due to poor opening strategies. That’s not to say he played badly in all his games, rather, in some games, he took unnecessary risks as he tried to transition to a playable middle game.
As an example of when his idea worked, in round one against Jose Capablanca, he launches a novelty in the QGD that spooked the stronger player into launching a knight sacrifice to play to a forced draw so as not lose.
In round 5 as Black against Ed Lasker ( two Lasker’s at this event… one, the BIG Dr. Lasker, the second, a distant relative Ed.), he manages to get behind in material ( pawns) out of the opening. He’s a strong defensive player and holds his ground. Later, he sacrifices a Bishop to gain entry to the weakened King and wins the queen and the game.
In round 7 against Bogoljubow, he inherits a cramped position out of the opening but has the bishop pair. Janowski had a reputation of being quite deadly with such a pair and proves true after a series of exchanges to free his game. He sets up a nice deflection tactic that squeezes out a win with vice like pressure on the 2nd rank.
In round 10 against Tartakower, a proponent of the Hypermodern defenses, he gets behind in material and is faced with an advanced passed pawn and strong knight outpost. In a do or die scenario, he exchanges his rook for the invasive duo and frees his game enough to later pull off a draw by repetition in an otherwise lost game.
As White against Maroczy in round 17, he gambits a pawn to grab a lead in development and initiative early on but then seems to squander it as he drops a central pawn. A misstep by Maroczy allows him to recover gracefully as he gets an advanced knight out post and traps his opponent’s rook and goes on to win the game.
Comments on his playing style by others in the tournament : ( source Wiki)
Janowski played very quickly and was known as a sharp tactician who was devastating with the bishop pair. Capablanca annotated some Janowski games with great admiration, and said, "when in form [he] is one of the most feared opponents who can exist". Capablanca noted that Janowski's greatest weakness as a player was in the endgame, and Janowski reportedly told him, "I detest the endgame."
American champion Frank Marshall remembered Janowski's talent and his stubbornness. In "Marshall's Best Games of Chess" he wrote that Janowski "could follow the wrong path with greater determination than any man I ever met!"
Edward Lasker in his book Chess Secrets I Learned from the Masters recalled that Janowski was an inveterate but undisciplined gambler who would often lose all of his chess winnings at the roulette wheel.