It was just ok for me, dawg. It was slow, the dialogue was fine, but forgettable, and there wasn't nearly enough exposition on how Hamer and Gault tracked Bonnie and Clyde.
However, what it absolutely nailed was making Bonnie and Clyde feel like just another duo/gang of thieves and murderers. It trivialized them by not showing their faces until the very end of the film, and giving them very little screen time. Yes, they were notorious and crafty, and this film conveys that very well. They were not worthy of respect, or admiration, or tolerance, and this film conveys that very well too.
If you like dramas, it's worth a watch, but only if you've got nothing better to do than watch Nascar on a Sunday afternoon.