This will be my second Ad-Tech, I went to Ad-tech NY last year. An exhibit hall pass will suffice, the sessions are geared more towards branders/media agencies, on the floor is where you want to be. You can even even go to the keynotes with the exhibit hall pass if you wish.
As to what to expect; it's a lot more formal/corporate then Affiliate Summit and significantly larger because it encompasses all aspects on the online ad/marketing industry. In NY it took me almost a full day to get through the floor(actually several floors) unlike with ASW it took me under a hour.