What's so good about the current MX5?

[JoePublic]

The consensus seems to be that the mk3 had lost its way a bit dynamically, but the latest version is said to be back up there with the best of them, so just how wideranging are the changes that have prompted this?

Is it just a tune-up job administered to things like revised spring/damper rates and different rack mounts (for example) or is it more fundamental than that?