If you're interested in reading, I'd go hit the changelog and start about 2 years ago and skim through it for the major changes.
I think the demand distribution and plane is too small stuff have been in play for 2 years, so that's not super new. Small plane stuff has become easier when you're flying small and medium aircraft.
Basing rules have changed - game worlds generally have a 10 base limit with an aggregate limit of 600 planes (adjusted for year though) across all bases.
Plane costs are more dynamic and often do not make logical sense.
Sami-random events that sometimes make sense and sometimes don't have been added (showing up in world news and will impact demand).
Games now typically run until 2030.
Noise regs are now in play and enforced.
You can store aircraft in the desert.
We switched to accrual based bean counting.
If you start on page ~5 or 6 of the v1.3 changelog, then the new changlog thread, you should be good to go.