I will freely admit to being not even close to liking rap. I dislike it as an art form, which means that I'm automatically biased against any band that includes rap. It takes a lot to get me to like a rapper or even a rap-rock group. So it means a lot for me to actually say that I'm not against Hollywood Undead at all.
My sister is a huge fan of theirs, so I've heard pretty much every song they ever wrote at some point. I liked "Young" off of Swan Songs, but couldn't stand the rest of the album. It just sounded like generic party rap, filled with the group talking about how badass they are and how much they drink and all the bitches they fuck. It was boring at best and obscenely bad at worst. Obviously, I heard about their next album and wasn't very enthused. Even after hearing "Hear Me Now" as their early release, I wasn't confident that American Tragedy would be able to improve a lot. How wrong I was.
American Tragedy is a much better example of their potential. The fact that they actually play their own instruments instead of relying on a backing band or CD already indicated to me that they could do a lot better with their own knowledge of music, but American Tragedy is a complete turn-around from Swan Songs. The number of party songs has dropped greatly, and the album in general is much more cynical and introspective instead of just being a celebration of their informed badassness. Deuce wasn't a particularly bad singer, but Danny is a hell of a lot better (having alternative rock experience) and even has a nicer mask. They've added a lot more rock and metal to their sound ("Bullet" is, of all things, acoustic) and generally cleaned up the sound quality. Their lyrics still aren't the best you'll ever hear, but they're much better.
I think Hollywood Undead shows a lot of potential. American Tragedy proved that they can make something more than something to use a beer bong to, and they can make generally good mainstream music without losing their own unique sound. I've heard that their third album will be musically closer to Swan Songs, but I hope it doesn't mean that they'll lose the progress that they've made. Maybe they really are deserving of their chart position.