The biggest mistake is allowing former players to vote. Of course egomaniac quarterbacks are going to think it is the only position that matters. No consideration is given for great players on so-so teams, either. It has become a trophy for the most popular quarterback on a top 5 team.
I knew all I needed to know when Troy Davis of Iowa State lost to Danny Wuerffel of Florida in 1996. Davis was the only two-time 2,000-yard rusher, and Wuerffel was a system QB who was absolutely nothing special.
Some fans like to look at the pro careers to determine if the trophy selection was a good one, but the Heisman isn't an award for future pro success. The college game is different enough from the pros that the skills of a great player won't translate. Players like Dat Nguyen or Danny Woodhead might be incredible in college, but just not built to carry the same success to the NFL.