... I've only heard one good rnb song. No good country songs, no good j pop, and no good jazz.
You've probably just heard all the wrong stuff. For an example: I absolutely abhor almost all country, though there are a select few that I actually really like. There is loads and loads of music out there. I bet you'd at least like some of the jazzy video game remixes on OCR (Overclocked Remix). I used to think of jazz as music for old "classy" and boring people. But that was based off of hearing crap on the radio. Later I heard some amazing jazz and I really love a lot of jazz out there now, since I gave it a chance.
As for j-pop: I've found that it tends to be pretty girly and the vocalists like to use the heavily auto-tuned style (like that ring-a-ding-ding song and "Sorry Sorry", ect, I think those are j-pop). But, there are some j-pop songs that I really like that aren't so girly. In order to judge a musical genre, you really have to hear all sides of it, and there is usually a lot of variation (a.k.a. sub-genres) within a genre.
Btw, right now I'm liking: Pendulum's "The Island - Pt. 1", "Witchcraft", and "Crush", Yui's "Life" (such a great song and vocals, used in Bleach at one point ;3), some K-ON (the instrumentals by Hyakkoku Hajime), FamilyJules7x's "Snow World" (Castle Crashers cover) and his Pokemon covers, C.N. Blue's "Oetoriya", "Love", "In My Head", and many others of theirs, Kawada Mami's "Joint" (used in many animes seriously overused but a good song) and "Intron Tone", May'n's "Chase the World" (used to be the intro song for the Accel World anime), Dream Theater's "On the Backs of Angels" and others, Philter's "8-Bit Smiles", Steve Chou's "Guan Bu Shang De Chuang" (the only song of his that I really like; just real a beautiful and musically interesting song, but the music video will ruin's it cuz it sux).. and there are many others. Of course I listen to the "Battle of Life" fairly often (from the Heartsrings OST Special album) and I'm always searching for any other rock songs like it.
EDIT:
Ah, almost forgot: Been listening to Utada Hikaru's "Simple and Clean (Planitb remix)" because I'm really into Kingdom Hearts again atm (Playing KH2 right now, because it is one of the most incredible games of all time, seriously). And, don't kill me, but I'm also liking Nightcore's "Dam Dadi Doo" song.