Dallas tried the pacman experiment, had him on the cheap and he generally couldn't stay on the field. His skills simply weren't there. He's not in the NFL for a reason.
It wasn't a talent issue whatsoever. He was injured that year in the game against Pittsburgh and then unnecessarily suspended by Goodell for four games for an argument he had with a bodyguard (who was later fired by Jerry Jones because he started a fight with Pacman rather than making sure he wasn't involved in any altercations). His stats aren't usually eye-opening, but that's because most QBs - even the great Peyton Manning - won't throw his way. When he does get a touch, he has a great propensity for taking it to the house (on K/PRs and INTs).
I'm not being biased at all - ask any player who has played with or against Pacman and many will tell you he's physically the most talented/gifted player they've ever seen.