Cant really argue with Schuey's list there to be honest. LOtSB was the best single dlc, I have ever purchased (for any game). Kasumi and Overlord are also very good, and not much between them to be fair. I was a bit let down with Arrival.
I would play Overlord and Kasumi during your ME2 campaign, with the other two, post campaign. Thats me though. Some play Arrival mid campaign, but it doesnt seem right to me. I would have thought most people would definately tend to play LOtSB post campaign.
Id say its worth downloading the Cerberus Network too. (check if still free with new copies) The Normandy crash site, and Zaeed are both worthwhile. Personally, I never really liked the Hammerhead from Firewalker, although it looks good in the Normandy
Totally agree with Firepower pack too. The Mattock rifle is one of the best in the game. I wouldnt bother with the alternate appearance packs, unless you are a die hard fan, who must have everything. Waste a creds lol
Lair of the Shadow Broker is a must have DLC for Mass Effect 2 no doubt about it. It doesn't matter if you play it during the main campaign or after the final mission as it changes depending on when you play it.
As for the others ... pretty optional. If you're going to get Kasumi: Stolen Memories you may as well get it right away since having her as an additional squad member is kind of pointless after the main campaign. Her personal mission, while interesting enough,
is pretty short and she's not the most useful squad member in combat. Add the fact that she has no "true" conversations in the
Normandy and yeah ...
Arrival was a huge letdown and it looks like they're going to have Mass Effect 3 assume you completed it anyway. Your choice.
Lair of the Shadow Broker is definitely a must have DLC for Mass Effect 2. Stolen Memory should be played during the main game. Kasumi is a good squad-mate but the main reason is because you get the best SMG in the game. I guess Arrival should be played
to bridge the gap between ME1 + 2.