Only listened to it through 3-4 times, but I think it's excellent. Really (especially since it's the follow up to quite possibly the shittest Megadeth album ever - maybe the 2nd shittest). I think it's the most aggressive record since So Far So Good... and the new lineup sounds great. Kiko's playing really fits, like Marty v2.0. And I think Adler was the perfect choice, always thought he would suit Megadeth, flashy fills and awesome double-bass. Favourite tracks so far are "Dystopia", "Post American World", "Conquer or Die" (which is basically one big solo), and "The Emperor".
DISCLAIMER: I'm biased. But even so, if you don't rate this album you should probably never listen to Megadeth ever again because it's unlikely you'll be pleased / they'll release Rust in Peace 2.