I didn't find it gleeful. I think those disgusting elements were on purpose. We aren't supposed to be feeling "OMG, that's so awesome!" We're supposed to feel, "This guy has finally gone full-blown monster. He's an irredeemable monster, fighting irredeemable monsters." We didn't get that moment in the Netflix shows.
At least, that's my take away. I was uncomfortable with it, too. I think Blue Ruin did some of this a lot better, but I think that's the gist of this movie, too: giving oneself fully over to this sort of thing is bad for everyone.
(The pen-stabbing kill is a perfect example. There's nothing awesome about that moment, which goes on for a few beats. Compare it to Jason Bourne fighting with a pen: that's choreographed so well, and it's this big moment of "Wow! He can do cool moves with anything!" Here, it's just an utterly gross killing that they linger on the brutality and wreckage of for a moment.)