Ignoring the embarrassing amounts of edge and that there's manga that does this better, the MC is pathetic. If somehow he didn't see these stupidly evil assholes for what they were, then he's a gullible moron. 
The revenge story is also weak. Doesn't help that the flashback style ruins all the payoff and utterly fails to make me feel anything.  I don't enjoy Shield Hero, but at least they took time to set things up first by actually generating ire towards the villains.