Can't really say how good he is since I don't really see him making any major decisions as of yet. NX, Pokemon Go, Nintendo games on mobile were all started under Iwata, I believe even things like opening up Nintendo IP to theme parks was also under Iwata.
Yamauchi was Nintendo's best president IMO, he was a pure businessman who was smart enough to delegate to the West and allow NOA to be strong and adaptive. His main mistake was not insisting on CD-ROM for the N64 (IMO I bet Miyamoto played a key role in cartridge-only, which basically gifted Sony the market). This is largely where most of Nintendo's problems stem from, that one (really) bad decision.
Iwata was a really nice guy who brought a great deal of warmth to Nintendo, but under him Nintendo went way too far into their Japanese cocoon and let the company be run wild by creative fetishes and chasing the next gimmick rather than sound business philosophy. As a result Nintendo had incredible highs but suffered some devastating lows as well.
I think Kimishima is not trying to rock the boat too much. He's going to try and cement himself in the position for 2-3 years, then he will probably be able to greater flex his authority, but I doubt he's coming into this upending pre-existing plans and telling people how to do things. I think he's well aware if he over-reaches, he could be replaced very quickly by someone else, so smarter for him to bide his time and hope the late Mr. Iwata's iniativies (mobile, NX, theme parks, movies) can bear fruit. Then he'll be in a much more comfortable position to consolidate leadership.
