He explored many issues, e.g. what happens when robots misinterpret the laws, or what should very expensive robots do, or what happens if robots interpret emotional pain as "harm", but I'm not sure he investigated the obvious, yet extremely hard issue of encoding the laws from human language into computer program.
In the books the robots adhered to the laws strictly. The problem was that humans were able to circumvent the laws rather easily. For example; lie to the robot or divide the murder trough many robots each unaware of each other.
In absence of humans the robots were perfect for deciding moral subjects( as long they have enough information ), the opposite what tomp is suggesting.