Jackson did all-right, all things considered, as HC of the Raiders. They made a mistake to fire him so quickly, imo. Not saying he'll be a great or even a good HC choice by the G-Men but should have gotten more time, considering that team fell off a cliff after that.
For what it may be worth (probably not much), when he was Raiders' OC in 2010, they had one of the better offenses in the NFL with Jason Campbell at QB, believe it or not.