You've made it outside the mansion and your car is waiting, but sadly you're on the wrong side of the mansion. Use blind rage for this part to take out the gang members in front of you, on balcony and the guys on the far right as well as taking out the first few guys around the corner, because it makes things so much easier. After you get around the corner, the fuzz will turn up, so you've only got about three minutes to make your escape, meaning no time to dawdle. Take out the guys rushing towards you and note that in the alcove there is a medical pack for you to use or indeed come back to. Take out the guys coming up the steps and keep going.
One of Tony's pets comes and takes out one of the gang members for you. Take out the rest and head on up to the open area, which can be rather hard to clear as there will be gang members everywhere. Your blind rage should be nearing full at this point, so use it when you can. Head on up the steps making note of the health pack if needed, and go through the gate taking out the guys in your way. Head into the maze and be careful that nobody sneaks up behind you in this circular maze and take out the numerous gang members waiting around. Make use of the cover (the hedges can block bullets). Of course this is a good time to use blind rage if you have it (if you didn't just use it in the open area). Now get out of the maze and head up the stairs where a cut scene will take place and the police will come and take out the remaining gang members while you make a run for it.