The interaction between the 2 is where it's at though, unsurprisingly.
Like, both can act like edgelords occasionally, then they complement each other's lines, they bicker at each other, and they insult and threaten each other seriously sometimes, and in the end one of them has to die. Despite that fact, they both are pretty optimistic about their situation and plays along just fine, as each of the 2 is entirely confident that they can win the contest.
I wouldn't say he's a bad character in that regard really.
His general theme of "demonic scythe" is really, just okay. Like, it's Garen level. Not something spectacular, but it's not just flat out bad either. It's "expected" and just "okay", is what I get out of his visual presentation.
Some people get overly critical on him because of the scythe and his supposed "edge" or something. But really, if you push out all the existing prejudices, he's just an average and stereotypical champ like most of the ones on the roster (though his E is gonna be so hard to balance).