although I like mianly rock music I'm always impressed by a well executed instrumental
one of my favorites is classical gas by Mason Williams - but also apache and wipeout
but there is also genius to be found in licks, riffs and intros
I particularly like buzzsaw guitar intros - think anthrax by Gang of Four, Bela Lugosi's dead by Bauhaus, High voltage by AC DC, Holiday in Cambodia by Dead Kennedy's
I think that some of the great instrumentals in famous songs are provided by band members to the song writing team - guitarists noodling away with chops or drummers
however having had a go myself (with no very notable success) it does helps if you are able to think of the songs in terms of the chords (you may know a bit about harmony) and the associated scales
in short a back to front knowledge of the instrument is key but if you are not a multi instrumentalist theory can help