Official PlayStation Blog:
"My Peoples, it's no secret that PAIN is the People's Game. Our community has asked us for certain features or types of gameplay, and we've taken that feedback and turned it into modes, characters, bug fixes, and so on. No doubt, continued development of PAIN is a time-consuming process filled with pitfalls and turmoil, but in the end, it seems to be working out for the best. We never seem to be able to give you enough content quickly enough, but we get some quality feedback every time we release new content (not just praise – constructive criticism is welcome, too).
We're about to drop the Smack Pack on you (sold separately), which includes the Darts and Fortress game Modes..."