You know, Destructoid's review of Arrival, the last bit of Mass Effect 2 DLC, is so on the nose with how I felt about it that I'm taking the lazy way out and simply saying: read what they done wrote.
In short: play it post-game, if possible. It lacks the emotional punch it could have had, but it's still a nice universe-expanding set of events, and it's got me all jazzed for Mass Effect 3 (like i wasn't already). It's nowhere near as good as Lair of the Shadow Broker, but then, what is? LotSB is pretty much the best piece of DLC ever. Unless you count Red Dead Redemption's Undead Nightmare, but whether you count that or not is your beeswax.
Anyway: worth the 560 MS points? I think so, but then you know how I roll with Mass Effect: I roll NERD.
I don't really know what that means, sorry.