I am currently listening to this (thanks to Nithya's recco for the whole album, which I strongly second). Personally speaking, YSR seems to be good at this genre. Another of his earlier numbers, this one from Raam, was impressive too. For some reason, I listened to Boom Boom only when I watched the movie and it did not stick. But I saw the movie twice on successive days and soon I was humming it all day. Ok, parts of the song did make me cringe - especially the references to Britney Spears, Norah Jones and George Michael, but it helped that the song was picturized very well and that made me react positively.
Nithya says she does not exactly care for Yuvan's voice usually and yeah, I agree to this too. His screeching is definitely cringe worthy (case at point 18 Vayathil in Kadhal Konden, Idhu Kadhala from Thulluvatho Ilamai and the yodelling in Nizhanil Nijamum from Raam). But his voice is unusual and suits these two numbers, possessing Shaggy-esque tonal traits, if you ask (the "inexperienced in hip hop or any other kind of non-Indian music") me.
I remember reading sometime ago (on one of The Hindu's Take Two series of articles?) that he was working on a Tamil hip hop album. Going by these two singles, that album could set trends.
Hey yo, Yuvan, you there? Yeah? Spin that shit up... soon!