The difference between comparing Buffy and Angel is that they are at least similar shows. Firefly and Dollhouse have nothing to do with one another. The only thing they have in common is mutual writers, directors, a creator, and an actor; You cannot compare them in this way and be fair about it.
On top of that, Dollhouse was not cut in the way Firefly was. Dollhouse had warning it was going to get canceled, and they set up their second season as such. Because of that, Dollhouse's ending was much more fulfilling and encompassing. Firefly had Serenity, yes, but at the end of the day, there were still many, many plot lines that didn't get seen through.
Again, though, they are completely separate shows and it is ridiculous to try and compare them.