The plot: An ex-con looking to go straight is blackmailed into one last grift.
I'm a huge sucker for film noir, so it's not like I could pass up a chance at watching a gritty crime thriller with Sam Jackson. I was a bit apprehensive when I saw the critical disdain, but I figured it'd be worth a try. I think some of the critics were a bit harsh, but this isn't really a great movie. There are certainly some good aspects to it, but the aggressively derivative elements really drag down the score. If it had been less of a pastiche (and outright ripoff) of certain movies, this could have been good. Unfortunately, to mention its primary inspiration would be a huge spoiler.
If you're tolerant of "homage", not looking for a unique story, and are a fan of either noir or Sam Jackson, then there's a fair chance that you'll enjoy The Samaritan. I found it quite watchable, but I was not impressed with the directing or writing. The acting, on the other hand, was fine. There are only two or three scenes with Sam Jackson's trademark outbursts of angry yelling, so you might want to load up Pulp Fiction again if that's what you're looking for.
Any true Sam Jackson fan has sat through some really terrible movies. This is nowhere near the bottom, but it's somewhat frustrating in that you can see how this could have been a good movie if they'd tried a little harder.