The Rules of Warfare was updated in January. Any rule changes since then are in the current FAQ. (Both can be downloaded from WKs site)

The big items are:

Failed capture of a mech causes damage to every unit in a formation

A mech that successfully breaks away deals 1 damage to all enemy infantry in base contact

Mechs ignore infantry bases when moving

Artillery deals its printed damage to all units within the blast radii of their targets - this damage does not combine or 'stack' in any way where blast radii overlap

A unit that charges receives damage equal to half their primary damage, rounded up (this includes heat effects, but not brawling)

There is no first turn immunity

Orders are 1 per 150 points. A standard army is 450 points. Awe is one roll per 450 points.

A game is 50 minutes long. (goes into effect soon)