Disclaimer: I understand that he is only a clone, so I should treat him as such and NOT complain about his inclusion over Ridley, Mewtwo, etc.
Personally, I didn't find him that interesting in Uprising. Like at all. He was the most generic and predictable baddass, "I fight for no one," type of clone character I have ever seen, even compared to characters like Shadow. In fact; him and Palutena were two of the characters in Uprising I found the least interesting. So, character-wise I don't find him very appealing at all.
Yeah, he's a clone, but I can't fault Sakurai for adding in more characters last second, but why him? Why would he want to add a lowly requested character from an obscure franchise that already has one, very popular, and very unique newcomer? Seriously, Donkey Kong and Metroid get no newcomers and only two slots, while Kid Icarus gets two newcomers and three slots!? I'm sure Dixie Kong would've been a way more interesting, popular, and deserving newcomer. Dark Samus has been in three times the amount of games Pittoo's been in, and reps a franchise in need of more reps. Even Alph, who is already programmed into the game, is an alternate costume and not his own character while Dark Pit is? I just don't get it. And like I mentioned earlier: the KI series already has a newcomer, but DK (DIxie Kong), Metroid (Dark Samus), Pikmin (Alph), and Zelda (Impa), which are all more successful series, have no one.