
A Century of Chess: Akiba Rubinstein (1920-29)
The chess world had largely moved on from Rubinstein by the 1920s. He was poor, he was strange, he was slowly going crazy, and he was not at all a participant in the flashy theoretical discussions underway. As Tartakower wrote, "His tragedy consists in the fact that the logic, upon which he had during his years of fervent study based his entire art, has been disintegrating and being replaced by the fantastical in chess." The decade featured one slight after another — he wasn't able to raise the funds for a potential world championship match in 1922/23, he wasn’t invited to New York 1924 — and, since everybody knew that he would never be able to raise the funds to challenge Capablanca, he gradually slipped out of the world championship discussion even though he by all rights fully deserved a match.
For all of those reasons the historical assessment of Rubinstein usually stops around 1914, when he had his poor showing at St Petersburg, and unfortunately that neglects a long period of consistent top-level performance during which Rubinstein seemed to head deeper and deeper into the innermost secrets of the game.

With Rubinstein, there is never anything superficial. Tartakower described him as "more than the other great matadors building the monumental in chess — producing games interwoven with a single unifying thought." He specialized in exactly those positions that are most enervating to the average player — long, slow endgames; ‘simple’ positions where one must proceed square by square and the slightest mistake eradicates all one’s hard work. Rubinstein’s deficiency as a player was that he started relatively late and didn’t have the god-given tactical ability that some of his peers were graced with. As he got older, the slippages increased and that kept him from winning as many tournaments as he otherwise might have, but his record was still remarkable: second at Gothenburg 1920, third at The Hague 1921, fourth at London 1922, first at Vienna 1922, which was one of the more impressive tournament performances ever, second at Baden-Baden 1925, shared first at Marienbad 1925, third at Dresden 1926, shared third at Bad Kissingen 1928, fourth at Karlsbad 1929, second at Budapest 1929. And if Rubinstein’s play was fundamentally positional, he also showed that he could light it up with the best of the tacticians.

Rubinstein's Style
1.Wild Man. "It is greatly to Petrosian's advantage that his opponents never know when he is suddenly going to play like Mikhail Tal," Boris Spassky observed of Tigran Petrosian and the same was basically true of Rubinstein. I’ve never seen it really explained why he made the King’s Gambit part of his opening repertoire — maybe he felt that more tactical play could increase his funding and his chances of a world championship match or else he was bored of his own overly positional play or else he thought that a tendency to mix it up might be a psychological advantage. In any case, the King’s Gambit — and combinative play in general — suited Rubinstein more than anyone had a right to expect.
2.Square by Square. This is Rubinstein in a more familiar element, starting from quiet openings and simple positions and, like a cyclist on a long-distance race, just slowly inching forward, taking squares, cutting off his opponent’s counterplay (even when it was very clever as in the case of the Bogoljubow game), and getting the tactics to flow from a superior and sound position. Rubinstein’s games in this vein give the impression of being very close to the deepest truth of chess.
3.The Endgame. The complement to this kind of patient, careful middlegame is of course a patient, careful endgame, and Rubinstein’s play in this phase of the game reached computer-like levels. What is noteworthy, besides his patience, is his ability to win from incremental advantages and, as often as not, to win by a tempo. His game against Brinckmann in particular gives the impression of being something like a mathematical theorem.
Sources: Donaldson and Minev's The Life and Games of Akiva Rubinstein is the classic book on him. Edward Winter writes on Rubinstein here.