I find the term "edgy" very questionable. Mostly because nowadays, it's just a buzzword. I didn't like it when people threw it around with Sasuke or some of the Uchihas in Naruto, because that's dismissing a lot of nuance that goes into fleshing out the characters to begin with, and I don't really condone the use of it outside of using it to describe someone using those tropes associated with it just for the sake of using them and portraying it completely over the top in the most non-sensical ways possible or portraying them so by the books that it's been overdone to death.
In that respect, I could give the same criticism to Den-O for being completely dumb when it didn't need to even need to be in it's own runtime. Not to mention, Kai appearing out of nowhere during the last arc just detracts it from ever being anywhere near as good as Kuuga ever was. Like, Ryuki and Blade, despite whatever shortcomings they had, still managed to make up for it by giving a very satisfying ending, or multiple versions of the ending itself. Den-O's Kai arc felt a lot like Kabuto's last arc with the last boss being Mishima. Out of nowhere. At least with Kabuto, Mishima was kind of always around from the start, with Kai it was just implied that Ryutaros was sent by him, but that was never mentioned nor hinted again until it kicked into full gear.
Kuuga still did it best. The confrontation between Daguva was built up since episode 1 since he revive the Grongi, and when you finally get to that last episode, no OST or any other flashy noise was needed. It was just pure catharsis to see those two finally duking at it. The Death Imagin on the other hand? Yeah, I don't know, I always tend to say a story's greatest asset is what it's main villain has to offer and how closely they tie back into being the antithesis of the main protagonist that's been shown so far.
Den-O's concepts are great. It was probably one of the most unique in terms of Early Heisei. But concepts alone do not make up all of story telling. I think Kobayashi just had a bunch of these great concepts in place but didn't flesh them out as neatly as she could have because of how much the show just focused on the it's dumb comedy to make people laugh rather than going into lore building.