"Under Cover Of Darkness" has one big thing going for it, and that is it's very quick, and aggressive Guitar chart.
It barely lets up throughout, constantly throwing double strums at you, starting off with simple bouncy single note strumming, and a few chords, followed by some very fun, slightly offbeat hammer-on strings that you travelling from the left side of the freboard, to the right and back again with plenty of bouncy strumming in between.
Then the meat of the song kicks in, a very rapid series of chord and single note switches that keep darting up and down the fretboard. This is were the song may alienate some of the less experience Expert Guitarists out there, as while most of the chord changes are pretty standard, there are a few really unusual pattern changes that could easily frustrate newer players, such as green to green and orange chord switches, and even rapid three note chord changes in a row that you very rarely see in Rock Band.
Then you rinse and repeat, but with one other thing worthy of note, a surpsingly laid back guitar solo with plenty of movement back and forth as you hit steady single notes, sustains and a few hammer-on strings that snake back and forth across the board.
Overall, this is a solid chart. But I can see this chart annoying some of the less experienced Expert players, so depending on your skill level I'd recommend looking at a chart preview first on youtube before diving in.