QPR are top of the Championship table after an unbeaten start.
"It is pretty much an unrecognisable team from last season," Green told BBC Radio 5 live.
"The manager has done a great job in the change of personnel and acquired people who are going to do their utmost for the team."
"It is a league which isn't easy and no-one underestimates," added the 33-year-old stopper.
"We are slightly guilty of underestimating last season.
"It is a tough league and you need certain personnel to have a successful season."