We were there last year, and probably made the mistake of choosing this to be our first time at MK. We thought it was very crowded, however, we walked on all the rides. We all dressed up, but went with the attitude that we wanted to do all rides possible, since we had never been there before. We walked on BTMRR 3 times in a row. The only thing we waited for was SM, and that was about 10 minutes. We trick or treated as we wanted and as we left for the night there were CM's by the park entrance giving out huge handfuls of candy.
My only advice- don't make this your first MK experience- we really rushed thru all the halloween events in order to do rides and probably missed half the fun!