And if you are talking about flying, the two biggest differences left out or not well emphasized in the above posts are:
1) frame rate when engaged stays steady in AH. No stttuuutttuuuutttteerrr to single digits when trying to engage over contested areas. Note for Brooke - GeForce 6800GS won't help.
2) View Distance is greatly increased (six plus miles or more seemingly). In WWIIOL, your FE doesn't even render a dot at anything over 2 1/2 miles, forcing air-to-air combat to all take place where you can count on finding an aircraft to fight - which is typically < 3000 ft over contested towns. Add in the smog, and air-to-air is completely ahistorical and mind-numbingly frustrating.
Generally, as has been stated, AH is 10x better if you are a pilot. BUT! It's mediocre (at best) in comparision if you enjoy the virtual groundwar in WWIIOL. I can't wait for the "whenever" when someone does both great. I have no ill will towards the Rats - I hope they pull it off. I just got tired of wading through turds while waiting.