No one really knows mate... But I'm sure that they would have balanced it out perfectly :)
I will be playing on Hard mode as I like a challenge, not that Hard mode will be a challenge for me :P hehe
I think Shepard will be involved since they would have started making hl2 when OpFor was being made or something.. so im sure they already had the basic foundations for the overall story set... So i would say Shepard would be a key player in hl2 imo.
I saw one screenshot which had Squad: Following on it... This leads me to believe that you will be abel to give your squad orders such as:
Follow, Hold Position, Attack, use object and so on :)
weld pieces of shit to sides of buildings then climb up onto building... then escape from teh map >_<
seriously though, if its in the game, u would only be able to weld to certain materials ;)