DingBat does not have a good point ; Yamamoto was not outfought in a fair fight during the war - mostly because he never actually comanded a fleet in any so-called fair fight. He was not a "field" officer, so to speak - and in his role of planning strategies, he did quite well with the limited resources he had.
Yamamoto masterminded Pearl Harbor (yes, he had help from Genda and co, most general does) and his Midway plan was quite good - but two factors played out on him. First being the american having broken the japanesse code, second - and more important even perhaps being the fact that the US Navy had one of those unbelievalbe strike of good luck. On papers, no matter how you look at it, EVEN with America aware of the Japanesse plan, Japan should have won.
Only, the plane that was to check out the very area of sea were the carriers where didn't take out in time due to a technical failure on the cruiser Tone. This caused the whole mess with planes being rearmed by the time the US attack force arrived.
Only, the Japanesse Zero, which would have BUTCHERED the dive bombers in any given circumstances, were already at sea level intercepting the torpedo bombers when the dive bombers showed up - because the American planes had gotten separated during the flight and through random luck arrived with a perfect timing - it was NOT planned out.
IE, no one can fault Yamamoto for the failure of his plan there, except for a few minor details. The US Navy winning Midway was a one-in-a-million shot. America won the lottery, so to speak.
Yamamoto's other campaign was Guadalcanal and the Solomons, were *SEA* battles swung one way and the other, without any sides being able to claim a clear edge there - Japan lost a battleship or two, and maybe a few carriers (not sure on the carriers, I would have to check) but the US lost the Hornet and Wasp, got the Saratoga badly wounded (again) and even the Enterprise had to be removed from operation for a while due to damage.
Yamamoto was never in direct command, but most of his plans were quite good. Pear Harbor was a mistake overall, he knew it (Sleeping Giant quote), but Japan had decided to go to war with America, and it was the best opening move to make - though Nagumo really blundered by not ordering that third strike. Knocking out the oil tanks and repairing dock of the Pearl Harbor base would have hampered the navy seriously. Not to mention that with the orders they were giving out at that point, they had at least a fair chance of luring out the Enterprise (and Lexington possibly) to attack - and taking THAT one out on day 1 would have been another major edge.
Yamamoto's plan was good, Nagumo blundred when it came time to set it in motion.
The plan for Midway was just as sound ; only the US had broken the "unbreakable" Japanesse code, which allowed the Navy to avoid the Aleutians trap, and the USN was, as said earlier, extremely lucky.