The writing is bad in multiple ways. Worst of it is that there are constant info dumps with lengthy power and item descriptions taking up entire chapters at times. When it isn't boring me with info dumps the actual writing itself is rather boring even the fights which are drawn out like the worst DBZ fights. Finally it is also just bad in that there are often mistakes, missing or nonsensical sentences and it is just bad like a very bad translation. I can't say too much as I'm at chapter 27 and due to all the info dumps and drawn out worthless fights there has barely been any story progress. What little is there isn't good, but who knows maybe it become good at chapter 100+, but I'm not sticking around until then to find out. Characters, well so far the only character not a cardboard cutout is MC and MC isn't good. His character makes no sense given what little we know about him. He is reincarnated in for 6 years without memories then gets back his memories from his past life(though we have no clue what he was like in that life) then he has to live through Gilgamesh' entire lifetime of memories including Gilgamesh' feelings at the time yet comes out of it completely without combat experience or any other effect from experiencing all these memories that are probably even more numerous than those of his previous life. The world so far is fine, it's DxD. Can't really take credit for someone else's work. Author's additions to this work so far have not been for the better.
While I would jump at something like this. But I have to say it doesn’ suit my tastes. When you write the fic you decided on the character of Gilgamesh. However you diluted the character badly. You added a system onto it along with other powers. Other powers is fine as long as you keep the core power of the character. As when people see the Mc is gilgamesh they are expecting the Gates of Babylon. However since you have overloaded and diluted his character a lot. While he is gilgamesh the core of the character has become something entirely different and less rounded/dynamic character composition.
A decent novel but not for me Way too much rias and issei bashing The mc is a typical hypocrite who claims that he hates perverts like issei but a few chapters into the story and He's already lusting after most of the female characters The author made him to op but he lacks brains The fights are unnecessarily long