well actually there's only one uncommon time signature that works in a song and that is the 5 beats per one bar (5/4) which the band Dream Theater always use.you can put 9/8 or 7/4 or 11/4 but in the end it would all sound like the 5/4.I also listen to a lot of metal bands like you do. Rhapsody,Symphony X, ManOwar,as long as it gives me what i want to hear.And i agree with you,there is much more to music than theory coz music theory is just one thing man. there's also the Composition class where you will learn to make good melodies out of the chords or even the bass lines that you're using( a branch of Music theory), the Music Appreciation and Ear training Class which trains you to have perfect pitch. The Chorus class where the whole class is a choir, it will help you in blending notes making it sound very very good. The Solfege class where you will be singing some pieces in perfect pitch while using the note names as the lyrics. I studied these for 7 yrs before i became a Music teacher and a critic. and still i want more training so im planning to take my Masters Degree after a year or so to become a proffesor of music.. so if you are still taking classes then all i have to say to you is please do your homework and always practice coz you still have a long way to go, and also because that is what i always tell my students.