Whereas IREM Collection Vol. 1 had three shmups (X-Multiply, Image Fight 1 and Image Fight 2) Vol. 2 just has one -- Air Duel.

FTA:

Air Duel is a perfectly serviceable vertical shooter with some entertainingly detailed enemy fighters to coo at, as well as some memorably apocalyptic backgrounds in later levels. Otherwise, it's just a little bit lame, just there.