Yes

If you can, get Overlord too.

I've only played LotSB and Arrival. LotSB was an extremely solid few hours of gameplay, with some really snazzy environments, a lot of fun dialogue between Shepard and Liara, and an interesting new base location once you complete it that has a lot of cool backstory on the various characters of the series. Arrival isn't quite as good; it's much, much more combat-focused, and in fact the mission doesn't even let you bring squadmates along. Still, it's not bad; it's just a little underwhelming. It also doesn't help that it sort of undermines the plot of ME2 by providing a much more immediate, dangerous threat than the Collectors.

I've heard good things about Kasumi; of course she's more worth it if you're planning another full runthrough since, hey, squadmate.

Arrival sucks. Sure it sets up ME3, but it's really not enjoyable.

LotSB is a must have, as is Overlord IMO.

Kasumi's mission is pretty short, but neat.

Arrival is my least favorite ME2 DLC, but I still enjoyed it.