To put it simply, this updates the NHL, KHL, Swedish Elitserien, Swedish Allsvenskan, Finnish SM-Liiga, AHL, ECHL, CHL, IHL, OHL, British EIHL, EPL, ENL to the 2009-10 season as well as the WHL, QMJHL, NCAA, Swedish First Division, Swedish Juniors, Russian, Czech Republic, Danish, Norwegian, Swiss, German, Slovakian, and Austrian rosters to the 2008-09 season. You can find a more detailed list of changes in this thread.
Lidas has spend somewhere between 2000 and 2500 hours work (that's the equivalent of 100 days working 24 hours) on this so please be sure to thank him here. Without his annual update EHM surely wouldn't have anywhere near the longevity it enjoys.