The MiG-29K features a totally redesigned wing and leading edge root extension, beefier landing gear, a modern glass cockpit and the proven and upgradable Zhuk-ME radar. It also carries much more gas than the "legacy" MiG-29 (40% more internal fuel), includes a full fly-by-wire flight control system, has true multi-role capability and includes a high-degree of sensor fusion, at least for a Russian design. All of this comes in a package with the ruggedness that is a hallmark of MiG designs. As a comparison, the MiG-29K is very roughly analogous to something between an F/A-18C/D Hornet and a early block F/A-18E/F Super Hornet.
MiG-29K seems like a rational mix of capability, size and cost (unit cost around $32M). It also offers the multi-role capability, relatively advanced weaponry and ability to act as a buddy tanker that have been lacking in past Russian naval fighter designs