Interesting or intriguing is in the ear of the listener so I'll leave that judgment to others, but there is nothing complex about any of the songs I listened to. The instrumental metal jam basically goes back and forth between two chords (although the two chords change occasionally) and the acoustic jam in Am circles the same tonal center.
The metal song was the first song I wrote.
Give me a little bit of a break on that one. The acoustic jam has wiered chords in it that I wouldn't have thought to do from my theory knowledge. It doesn't change keys or do anything out of the ordinary but it sounds nice.
If you want to hear good examples of 10-20 minute epic pieces, listen to old Yes, Emerson, Lake and Palmer, Camel, Spock's Beard, Ozrick Tentacles, Miles Davis, etc. I'm sure other's can make suggestions also.