The most underrated naval commander was Raymond Spruance, who assumed command at the Battle of Midway following the damage to the Yorktown, and commanded at the Battle of the Philippine Sea in June of 1944. Overshadowed by Halsey, he never would have fallen for the Japanese carrier lure at the Battle of Leyte Gulf.
As for underrated battles, probably the most decisive underrated battle was fought prior to WW2 starting, between the Japanese and the Russians at Nomohan/Khalkin-Gol on the northeastern border of Manchuria. The Japanese decided after their shattering defeat by the Russians that it would be safer to attack south for resources to sustain the China war than to attack the Soviet Union.
The other would be the campaign to isolate Rabaul from August of 1942 through February of 1944, which aside from costing the Japanese heavily in irreplaceable warships and transports, also essentially destroyed their carrier air power far more thoroughly than the losses at Midway.
Lastly for simple unbelievable guts and determination, the low-level attack by B-24 Liberators on the Ploesti oil refineries on August 1, 1943.
