Bioware seems really to have listened to the Biowarians on their Mass Effect forums. Everyone seems to have wanted Batarians. And Bioware did give everyone - just that - Batarians.
OK, it was perhaps not the quest or mission I would have used to introduce Batarians, but now we have Batarians in Mass Effect - for 5 US dollars. A 90-120 minute (Premium) module content seem OK to me - at least it is way better than Oblivion's Horse Armor for 2 US dollars or some other DLC content for Oblivion.
On the whole 'how many hours do it take to finish a game?' here is a website to get you thinking:
http://speeddemosarchive.com/GameList.html
As you can see Fallout can be done in 9 minutes….
No info on Mass Effect so far, though…