Iwata had his share of successes (Wii, DS, 3DS) and failures (Wii U, and maybe even the Gamecube), but he always struck me as a leader that learned from his mistakes and tried new things. While he was the handpicked successor to Yamauchi-san, I felt Iwata was constantly at odds with the old guard culture at Nintendo who is now represented by his replacement Kimishima.
While there's no arguing that the Switch is Iwata's brainchild and the hardware/online controversies plaguing Nintendo have pre-dated the Switch, I also have my suspicions about the recent business policies of the system and that a lot of the recent baggage wouldn't have happened had he been alive and well.