Shoot 'em ups were certainly pretty abundant on Sega's 16-bit power-house and they were definitely of varying quality but one of the finest must surely be Hellfire, one of Toaplan's few horizontally-scrolling efforts. It was never the flashiest game around but it did have one vital ingredient - a great first impression - and a big reason for that was the fantastic music, composed by Toaplan stalwart Tatsuya Uemura, that blasted out at you as soon as you undertook your mission. Games like Thunder Force 3 and Super Fantasy Zone have better overall soundtracks but few shmups on any system get you pumped-up for the alien smackdown like this one does. See if you agree! (full Hellfire review here)
Special Note: I didn't record this great tune myself, I'm just an admirer, so all credit to, firstly the original composer, and secondly the YouTube user who uploaded it!