Its incredibly repetitive pop drivel. I wonder if teens have a higher tolerance for repetition than adults. They seem the only demographic with any affinity for this type of stuff.
I listen to a lot of trance/techno music and other similarly repetitive genres (eg http://www.youtube.com/watch?v=jrAxmOvjSYw&feature=relat...). But I like it to have a few different elements to cycle between, and when there's a big musical build I expect it to climax with something other than the exact same thing that came immediately before the build. I have literally made more interesting things than this over morning coffee, and I don't consider myself any great shakes as a musician.
The only explanation I can come up with for the release of this tune is that the quite-talented Rihanna was either incapable or unwilling to go back to the studio to record anything and there was a looming contract deadline imposed by her record publishers, so her management team took some abandoned recording material from a previous session and farmed it out to a momentarily-popular DJ.
There is also, in general, more tolerance for repetition in dance music than in other genres.