Yamaoka's best work is Contra: Shattered Soldier and even then he's outclassed by Sota Fujimori's songs on that soundtrack and the superior Neo Contra album.
He's pretty mid at sampling since half the time he doesn't even really do anything special and he really likes to reuse material. Replaying Shadows of the Damned and I recognize so many samples and drum beats from the latter day Silent Hills which was already something I found annoying with those titles.
I also believe he's not exactly hot shit on guitar either and what you hear on the records is a session musician. My only evidence is his live performances, a quick clip from a 20 plus year old making of SH2 documentry that shows someone else wailing on the guitar and whatever the hell is going on with some of the guitar playing in SH2 remake that sounds closer to the live performances.