At Metacritic, which assigns a normalised rating out of 100 to reviews from professional publications, the album has an average score of 83 based on 15 reviews, indicating "universal acclaim". At AnyDecentMusic?, which collates reviews from more than 50 media sources, the album scored 7.9 out of 10, based on 17 reviews. AllMusic awarded it 4 out of five, stating, "Clocking in at just over 80 minutes, the epic Senjutsu is another distended late-career triumph, albeit one that requires multiple spins to set up camp in your Homeric metal-craving cranium". Wall of Sound scored the album 9/10, calling it an "(...) epic and triumphant return for the lads... better balanced [than The Book of Souls]... with some interesting songwriting". The Guardian awarded it with the highest note and praising Senjutsu as "(...) an ambitious, eccentric master piece". Classic Rock’s journalist Dave Ling awarded Senjutsu with 4.5 stars out of 5 describing band’s effort as "(…) a remarkable album from a band that still has plenty to say and to offer".
