I play guitar. Mostly acoustic. I try to write my own music but I don't know what to do with the individual figures I write more often than not. Also, what I do write tends to be very obtuse and experimental. Spacey as hell, as well.
Music is the one thing that keeps me out of my thoughts because it's the only thing loud enough to drown them out, this being said, music has done wonders to keep me from getting too detached from this world. And I agree with that 5w4 as I am that.
Not all music has to be about feelings -- or what I called cliched 'sensitive guy with a guitar' lyrics, ie "Girl, your eyes are as bluuuuue as the sky."
Other possible topics for lyrics:
Religion or the lack thereof (we need more excellent atheist music; see XTC's "Dear God" sometime)
Triumphing over circumstance
Man against nature
The desire for power and its consequences
Sex (well, we INTPs are very sexual beings)
Achieving a higher conscienceness
Advocating for the rights of the downtrodden
Pride in accomplishment
The need for independence
Standing strong against the onslaught of a world which does not understand you
One of the reasons why metal is my favorite musical genre is that the lyrical content is often quite varied. There are ballads and love songs, but they're in the minority compared to socially-conscious songs (Rage Against The Machine, for example), or satirical, over-the-top humor (some of Type O Negative's catelogue) or even good ol' fashioned songs about Satan (see: Danzig).
"Study hard what interests you the most in the most undisciplined, irreverent and original manner possible." — Richard P. Feynman
"Never tell a person a thing is impossible. G*d/the Universe may have been waiting all this time for someone ignorant enough of the impossibility to do just that thing." author unknown