NVIDIA's process includes a phone interview followed by several levels of 1:1 in-person interviews at their place. Phone interview went well. First 1:1 went well (this was with the hiring manager). Second interview went well, I thought... No contact after second interview normally means the interviewer had reservations about the candidate. Followed up with the recruiter and received a "Thank you for your time" email several days later.
In retrospect, the snag was probably related to NVIDIA's matrix engineering organization and questions/concerns I had about being responsible for delivery/features/etc without authority over technical resources. As I understood it (and this is probably a simplistic summary), NVIDIA's Engineering Manager/DIrectors spend much of their time negotiating with peers to assign resources for their projects from a pool of technical resources (who report to another/different administrative management structure).