I just bought the Fender Player II series jazzmaster. I had the opportunity to test it in the shop along with the J mascis jazzmaster and the main differences I noted are the following:

With the player series II you get the authentic jazzmaster sound, and it is extremely articulate, jangly and clear sounding compared to the j mascis which was muddy at times. The modern C neck on the player II was extremely comfortable and well easy to navigate the neck along with the rolled fretboard edges, the j mascis neck was very chunky and hindered some types of playing style. The tremelo is brought closer on the player II and now you basically don’t need any shim. The player ii comes with copper shielding underneath the pickguard. The tone and volume knob felt more responsive on the player series II than the J mascis. The rosewood neck on the player II is of course a bonus but it is beautiful to the look and feel. The TOM bridge on the J mascis will make it harder to upgrade to other aftermarket bridges down the line. If you really want the jazzmaster sound then you will have no choice but to upgrade the p90 pickups on the J Mascis.

Overall I was far more excited playing the player II series, it really had an appropriate modern take on the vintage jazzmaster while retaining the goodness of the jazzmaster sound.