As for overall impressions on the song, I find it to be a bit weak sounding when compared to anything on the last album. Not weak in a poorly composed way, but weak in a thrashy sort of way. Let me explain; after 1990 or so, Megadeth started going in a more heavy metal sounding direction, rather than their previously thrash-oriented one. Personally, I think Dave and the boys redeemed themselves a bit with Endgame, as it was the thrashiest in a long time, but "Public Enemy" sounds akin to the heavy metal sound, instead of thrash. My initial impressions leave me thinking that the track could have been on Countdown to Extinction or Youthanasia. Both of those albums were actually very good, but I'm looking for a full on thrash assault, something I know I'm not going to get. I do think the galloping riff is quite nice, though.
I expect the studio version will rock my socks off and probably follow in the super heavy vein that Endgame enjoyed. If the band's upcoming album has a handful of listenable songs on it, I'll be satisfied. It's not like I listen to Megadeth for current material anyway!
Megadeth - "Public Enemy"