We have run multiple complete campaigns now, and the results have been interesting.
First, note that we have been making use of the conversion kit figures (monsters and heros) in all campaigns. Further, in each campaign that we have run, we have always used different heroes (none have been duplicates), we have mixed up archtypes and classes as much as possible (covering all combinations), and have utilized different open group monsters for each individual encounter. In addition, we have switched up roles in terms of who played OL and who played heroes.
All 2 hero campaigns (except for 1) have been landslide victories for the heroes. In all but 1 case, the heroes won every single ACT I and ACT II quest (though at times the OL won the first part of a 2 part encounter). The 1 exception involved the heroes winning every ACT I and ACT II quest, but losing the finale by a single roll of the die.
All 4 hero compaigns have been landslide victories for the OL. In fact, except for First Blood, the heroes lost every ACT I and ACT II quest (although 1 group did win the Interlude).
We just began a 3 hero campaign to see what differences this will bring. Given past performances, we suspect that the addition of a hero (and their skills) will out-weigh the OL's monster group limits mostly going from 1,0 to 0,1 (minion to master). We suspect the heroes are going to do well.
If you have finished campaigns, I would be interested to hear your experiences as to the number of heroes won, and who prevailed.