Actually retconning Dirge wouldn't be bad, or at least from canon to a gaiden.
I never played Dirge, so I never met Genesis from Dirge, but he wasn't too bad in Crisis Core.
Genesis actually only makes a cameo at the very very very very very end of Dirge of Cerberus in a post-credits scene. It was just them stamping more Gackt collaboration into the game (after Gackt's "Redemption" was used for the credits and his "Longing" was used for one of the final battles). Gackt portrayed Genesis in a live-action cutscene at the end, and that's pretty much how he was born. Square wanted to put Gackt into Final Fantasy. This, however, isn't where my gripes with him began. I didn't really mind it, and his
costume design was actually far better in Dirge.My gripes began with him in Crisis Core. Firstly, his
character design was simplified, to where he was just wearing a generic red coat with shoulder-pads. (In case you were wondering, Gackt DOES indeed voice him in the Japanese dub). Secondly, while his motivations began at first as something worth caring about (searching for a cure to his degradation), eventually he just became overly obsessed with a poem, to the point where he was just an obsessed fanboy.
Had the poem of Loveless been adored in the way poetry like
The Odyssey and
Hamlet are -- loved and well-known by the masses, and everyone knows what they are despite the fact that they're not widely spoken of in the general public -- it wouldn't have even been as bad. But Loveless is literature that was treated as if it were
Harry Potter or
The Hunger Games -- widely popular and talked about by a lot of people and plastered all over the media. Loveless' stage adaptation was one of the most talked about things in Midgar at the time, and I think they even mentioned a film adaptation in the works somewhere (though I might be wrong about this).
So in the end, it basically has Genesis come off as a nerdy kid to me. It'd be like Genesis thinking of himself as Ron Weasley, with Angeal as Hermione Granger and Sephiroth as Harry Potter. He'd probably even, at that point, consider Shinra to be Voldemort. Genesis comes across, to me, as a geeky fanboy, and in something like Final Fantasy VII, that doesn't make a good villain or even a good character to me (in contrast, a villain like that in something like Saints Row would probably fit in just fine).
On top of that, the fact that he quotes Loveless literally every time he's in a cutscene annoys the crap out of me.
His weapons and powers are really cool, though. I just hate the character of Genesis.
On a side note, the inclusion of Genesis and Angeal bugged me, because never at any later point in the timeline are these two EVER mentioned or remembered, despite the fact that they were two of the three First Class SOLDIERs, and even had their own fanclubs like Sephiroth. Plus, nobody even remembers all the destruction that Genesis caused in Midgar.