Not to downplay anyone's anticipation but I'm surprised people are looking forward to it.
Personally I thought DI was a mediocre game at best. I finished it(coop) and even though I like coop games this was one of the weaker ones. Despite the monotonous gameplay my main gripe with the game was the graphics engine, screen tearing, choppy framerate and overall unpolished was enough to turn me off from any possible sequel.
I'd wager the single player experience made the game better, at least atmosphere-wise. Personally I didn't have any issues with PS3 version, apart from a couple of inventory-related bugs (gear disappearing after modding, which luckily could be reversed by returning to the last save). I think the resort and jungle areas in particular were sights to behold.
Rap fit since it was the reason one of the characters was on the island in the first place. Fit the setting quite well of how things started with that little intro bit setting the mood of the island.
You could argue, that does the game need such a character, does it serve any actual purpose, or add anything to the game's theme? After all, he could have been a rocker, or a metalhead as well. Now, that I'm thinking about it, a reggae dude might have been the most fitting for the context. =)
I think a more traditional Hawaiian party tune would have been better for that party scene, especially if they wanted it to create a contrast for what was to follow.