I just got my Merkava kit on Friday and started removing and cleaning up the pieces. Its quite a kit and I'm happy to say the pieces are better molded than the original Legend Merkava IV kit, especially the tracks. The mold layout also improved with some of the pieces. Its easier to cut out the extra resin on some of the pieces.
Except for the molding issues though, there aren't too many differences in the kits. The new additional pieces include new PE and side skirts and a gunner's hatch in the turret.
Of course my experience with the first kit has helped me work through building this beast of a kit. I'd definitely recommend it for any Merkava fan.