In his book The Great Chess Masters and Their Games by Fred Reinfeld wrote "Dr. Euwe is the most underrated player in the world. Reuben Fine was absolutely correct when he made that flat statement in 1940." Fine observed that the opinion that Euwe won the first championship match in 1935 because Alekhine drank too heavily and that he lost the return match because Alekhine had restored his health was not true. Fine claimed Alekhine’s play in the first match was no worse than the quality he had played before the match. In the second match Euwe made a number of incredible blunders.
Chessmetrics assigns Euwe an all time high rating of 2769 on the January 1936 rating list and he was #1 on the list 14 months January 1936 and November 1937. True Chess analyzed world champions blunder percentages and on their list the author says the numbers say that Euwe was better than his reputation but, at the same time, his reputation as a player who blundered often is, sadly, richly deserved.
Lasker said of Euwe that he probably knew everything that was ever played or printed and that he was familiar with the teachings of Steinitz, Reti, Tartakower and Nimzovich. Botvinnik called him an impetuous, active player who liked to play on the flanks and was always looking for counterplay when defending. Euwe liked positions without weaknesses and 'makes disconcerting long moves,' aims for development, is satisfied with a better endgame, is subtle, has excellent technique, knows openings well and in general was a very good tactician. Smyslov, Tahl, Petrosian, Spassky and Karpov all had praise for his play and stated that early in their careers they learned from Euwe's books and games. Not a bad testimony about a "weak" world champion! I liked the following game...it's not full of tactical fireworks, but shows fine positional sense and was played with great precision and technique by Euwe.