The seats are the same as U.S. carriers, the meals are a little better with menus, and the staff is very attentive.
The lounge is very nice in Mexico City.
I have never flown on Mexicana airplane with entertainment enabled, so I can not comment on this.
However, on Mexicana you can do a revenue upgrade upon checkin and it is not very expensive. $50 to $150 depending on length of trip. So, this may be cheaper than actually buying the first class ticket.