I read some of the reviews here, and I think that some who have reviewed this extremely negatively (as in 1/10) are those who appreciate a movie with lots of explosions, and maybe some guys with their tops off, flexing their muscles to accentuate just how tough they are.
Luckily, there isn't much of that in Stand Up Guys. It's character-driven, centered on the relationship between Val (PAcino) and Doc (Walken), both of whom are spectacular.
There's some great dialogue between the two, and despite what you may read on here, the story is quite solid, if simplistic. I don't think people have fully grasped these characters in some reviews, or the meaning of the title "Stand Up Guys". They're throwbacks, and the situations they encounter represent the direction the world has headed over the years, a world that Doc is forced to be a part of, despite wanting a quieter life.
I won't go on any further, but I found the characters endearing, and the relationship between Val and Doc kept me on the hook.
Nice soundtrack, too.
Cheers