I haven't read up on the details of these but this is a huge step in the right direction if pulled off properly. The dichotomy between primitive and non-primitive types in Java is a real rough spot. I'd have to see how they deal with null values though because the introduction of auto-boxing certainly introduced a new area for NullPointerExceptions to catch the unwary off-guard.

There is extensive discussion of that topic in the valhalla-dev and valhalla-spec-experts mailing lists, but I think the details are still being worked out.